You are not what you say...

...but you can become it

Every one of us is born with a set of quality and faults. There are no people who have more qualities than others, but there are people who are born with qualities that are more appropriate to the world they live in. In the words of Albert Einstein:

“Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.” 

 You cannot change what you are. At best you can polish it and take best advantage of it. You can learn to play well with the cards you have been given. But from that to automatically assume: "oh well, I am stupid, I might as well face the facts", there's a huge leap.

There's a lot of quotes out there about how people judge you for what you are and not what you say. That is very correct. But what you do many times is influenced by what you think - and usually what you say comes from the same place. If you spend your life believing you are stupid, you will act stupid and therefore become stupid. Kind of like a self-fulfilling prophecy.

Let's put this in more practical terms: girl meets boy. Boy is cute, funny, can sustain a conversation (so at least within the normal intelligence levels) and seems to be very nice. Girl is interested in spending more time with boy - maybe even evolve to a romantic relationship. And then boy starts repeating as a theme song: "I am ugly, stupid, nobody loves me".

Of course, the natural reaction when you're in the girl's situation is to say "no, you're not". You say it once, you say it twice, but at some point a part of you is to start being annoyed. Because what you are saying does not register. The boy keeps repeating that he is worthless and that there's no point for him to try to be anything else than he is. He is not saying it directly, but he is suggesting that him and her will not work because of this reason.

From this point on what happens depends on the girl's capacity for patience. She can just say "to hell with this, I'm out of here", or she can insist on repeating "that's not true". But at some point, if something doesn't change in the boy's speech, the girl will leave. The boy will obviously assume "oh of course she left, I'm ugly and stupid and nobody loves me."

I'm not saying to go around advertising how awesome you are. There's only one Barney Stinson and his attitude doesn't work on many people either. Arrogance is just as annoying as defeatism. But in the above case, the girl did not leave because the boy was anything like he said, but because due to his low self esteem she was unable to develop a sustainable relationship with him. In the end relationships, as much as they are about compromise, should feel good to both people, rather than have one walking on eggshells around the other all the time. 

The above is not an example of modesty, it's simply someone giving the other plenty of reason to walk out.