Disappointments and Comparisons

Pastor says, we get disappointed because of what we expect to see. And not because of what we see. I guess that happens to me quite a lot.
Like, I would compare the responses of others to mine. Like what I would've done, given the same scenario. And when I feel I would have 'performed' better than them, I get disappointed. Or when, I compare what somebody else (of a similar capacity) would've have done in their case, and has done it better, I get disappointed.
But the thing is, why should i?
Shouldn't every individual be special and each circumstance unique in its own way? Why do we tend to compare?
What do comparisons do?
Comparisons make good references.
But what good is a comparison when it leads us neither to any references nor insights to the certain individual? Remember, each is unique. When you compare a person to another, you bring no value-add to him or her. So what if he or she is better/ poorer? We are not racing to break each others' records, only walking in our own pace, in life's journey (Some walk faster, others, slower. Nonetheless, its not a competition).
i learn:
Don't put anyone into a contest he or she never entered for.