The ability to distinguish sensations resulting from our own actions from those with an external cause is a fundamental aspect of human behaviour. This distinction is in some cases reflected directly in perception: for example, tickling oneself produces a less intense sensation than being tickled by someone else. – Predictive attenuation in the perception of touch
This explains why two people in a fist fight always accuse the other person of hitting harder. When each fighter throws a punch, his brain mitigates the sensation to his fist because he planned and expected the sensation. However, when another person’s fist hits him, he feels the full impact and therefore concludes the other fighter is hitting harder. What’s interesting is how this changes when we move from the physical to the relational.
A common fallacy about relationships is that they should be 50/50. Each person should give and take equally. Once again, our brains tilt the scales in our favor so that we always feel like we are giving way more than our 50 percent. We weigh every sacrifice or gift we’ve provided for another person. These things carry emotional weight and so we count them highly. When another gives us a gift or sacrifices, we usually have little idea about how much it cost them, and therefore, while we are appreciative, we downplay it’s significance. Another way to put this, is that our emotions are very real; we feel them. Others emotions can only be communicated to us through words and don’t carry the same impact.
The reality is that if each person in a relationship is only giving their 50%, both are going to believe the other person is coming up short. Maybe instead of 50/50 we should consider giving 100/100. Or perhaps, we should stop keeping track of what percent we are giving in a relationship.