By Chris Seiter

Published on December 29th, 2023

What if I told you that getting someone to commit to you could be solved with this simple equation:

“I = ƒ[A, B, S]”

“I equals f of A, B, and S.”

This is the equation of the interdependence theory.

So, what the heck is the interdependence theory?

Well, I’ll have Maria Mordvinova explain it,

Actually… the topic can get a little dry so let’s try a different approach,

Imagine you and your best friend are on a team to build a really cool fort. You’re great at finding the best wood and materials, and your friend is awesome at designing and putting it all together. To build the best fort ever, you need each other’s skills and efforts.

The interdependence theory is like this fort-building situation.

It says that in relationships, whether it’s friendships, family, or even countries working together, everyone involved depends on each other in some ways. Each person has something valuable to offer, like your skill in finding materials or your friend’s design skills . The theory tells us that the more each person relies on the other, the stronger and more important the relationship becomes.

So, just like how both you and your friend are important for building the fort, in any relationship, each person or group is important because they bring something special to the table. That’s why we often work better together than alone!

Ok, but where the heck does this wild equation fit into this all?

Breaking Down Our Commitment Equation

So, there are essentially four parts of this equation we need to dissect.

  1. I
  2. F,
  3. A&B (which will be combined)
  4. S

Let’s start with I,

  1. Interpersonal Interactions (I): Think of this as any time two people are talking, playing, working together, or even arguing. Basically, it’s any situation where two people are interacting with each other.
  2. Function (ƒ): In mathematics, a function is like a special machine where you put something in, something happens inside the machine, and then you get a result out. In this case, the ‘machine’ takes information about the people and the situation they’re in and then ‘produces’ the interaction.
  3. Actions and Characteristics of Individuals (A & B): These are the things about each person that affect how they interact. ‘A’ might be one person who is funny and loves to tell jokes, while ‘B’ might be someone who is really serious and likes to talk about books. Their personalities, moods, and what they do (their actions) all go into the ‘machine’.
  4. The Given Situation (S): This is where and when the interaction is happening. For example, are they at a loud party or in a quiet library? Is it a stressful time like during a test, or a relaxed time like during a picnic? The situation can change how people behave and interact.
    At its core the equation teaches us that the way two people interact (I) is a result of their individual personalities and actions (A & B) and the specific situation they’re in (S).

Just like if you put different ingredients and settings into a blender, you’ll get different kinds of smoothies, different people and situations will create different kinds of interactions!

So, ok the equation essentially explains how interactions work BUT they don’t really explain WHY people commit (yet).

For that we need to talk about something else.

The Investment Model Of Commitment

You’ve probably heard me talk about this in other videos.

I want you to think of the investment model of commitment as adding another layer to our equation.

Watch as I connect these ideas in a simple way:

  • Interpersonal Interactions (I = ƒ[A, B, S]): This concept, as we discussed, is about how two people interact based on their characteristics (A & B) and the situation they’re in (S).
  • Investment Model of Commitment: Now, think of a relationship as a garden that you and a friend are growing together. The Investment Model says that how committed you are to keeping this garden beautiful depends on three big things:

The Three Big Things

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  1. Satisfaction: How happy you are with the garden. If you love how it looks and enjoy your time in it, you’re more likely to stick with it. This is like how satisfied you are in a relationship.
  2. Alternatives: If you don’t have another garden or a better place to spend your time, you’re more likely to stay and care for this one. In relationships, if you think there’s no better option than your current relationship, you’re more likely to stay committed.
  3. Investments: The more you’ve worked on the garden, planted seeds, watered plants, and spent time making it nice, the more you want to keep it. In relationships, the more you’ve invested (like time, emotions, shared memories), the stronger your commitment usually is.

So, how does this fit with “I = ƒ[A, B, S]”?

Well, your interactions in the relationship (I) are shaped by both of you and your partner (A & B) and your situation (S). These interactions influence how satisfied you are, what alternatives you see, and what you’ve invested in the relationship.

Basically, how you and the other person behave and respond to each other can affect your happiness in the relationship. This behavior is shaped by both your personalities and the situation you’re in. If you’re happy, you’re less likely to think about leaving and more likely to feel that you’ve invested a lot in the relationship. These feelings help decide how much you want to stay in the relationship. It’s like caring for a garden – the more you work on it and enjoy it, the more you want to see it flourish!

Investment Is King

Yet, what if I were to tell you that when it comes to the investment model of commitment not all “qualities” are created equally.

Caryl E. Rusbult, a renowned sociologist (before passing away at the age of 57) had something interesting to say about all this,

The investment model of commitment is a predictive psychological theory that aims to explain why people remain in relationships.

So, technically speaking we can study which of the three main factors:

  1. Satisfaction
  2. Alternatives
  3. Investment

Seem to hold the most weight in why people STAY in relationships (even when it benefits them not to.)

And it’s here that investment truly stands out. Consistently in my research to figure out which of the three factors reign supreme I kept coming across this concept of a “sunk cost fallacy.”

Alright, so what the heck is this?

The Sunk Cost Fallacy Effect

The theory posits that the more you have invested in a relationship, the more likely you are to stay in it because you don’t want those investments to go to waste. This phenomenon is often referred to as the “sunk cost fallacy” in economic terms.

A 2018 study in Current Psychology , conducted by researchers at the University of Minho in Portugal, shed light on why people often remain in unsatisfying relationships. The findings pointed towards the sunk cost effect as a key factor.

The study involved over 900 participants who were presented with scenarios of less-than-ideal relationships. When faced with the option to leave these fictional relationships, the responses indicated a tendency to stay when substantial investments of money and effort had been made.

What’s wild is that these were fictional questions they were responding to AND THEY STILL WOULD CHOOSE TO STAY!

It gets even better.

Researchers have literally found a link between the sunk cost fallacy and time.

Like this paper by Anton D. Navarro,

In his study, he wanted to see if the sunk-cost effect – where people continue with something because they’ve already invested in it – also happens with time. He did several experiments using questionnaires (Experiments 1 to 4) and found that people do indeed show a sunk-time effect. This means people are likely to continue doing something they’ve spent a lot of time on, even if it might not be the best choice. He tried different situations, like changing the value of what they were doing, whether the decision affected just them or a group, and whether the time spent was enjoyable or not. In all these cases, the sunk-time effect was still there.


Navarro said he also did some experiments where people had to make decisions, not just answer questions.

These experiments showed the same sunk-time effect.


Navarro also found that when people felt personally responsible for the situation, they were even more influenced by the sunk costs in their choices.
And that brings us around to investment.

This in my opinion is the single most important factor to getting anyone to commit to you.

Investment comes in many forms,

  • Time
  • Emotional Effort
  • Shared Experiences
  • Financial Resources
  • Shared Goals and Plans
  • Personal Sacrifices
  • Intimacy and Physical Connection
  • Shared Beliefs and Values
  • Children and Pets

According to science, the more you can get someone to invest into you the better. So, theoretically what makes men (or anyone for that matter) commit is a combination of the interdependence theory and the investment theory.

Yet, the one key thing that seems to stand out above all is investment.

So, you want your ex back. You want that guy who doesn’t seem to be responding. Find a way to get them to invest time into you and statistically speaking, your odds go up.

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