What we call 'reasons' of not being with someone: "too plain", "so nerdy" , "lacking confidence", " unattractive", "not motivated", are actually our own judgements and the sense that we are "better" than them. And while it's good to have a healthy sense of self, it is important to ensure that in assessing someone, we are not being "too arrogant", "impatient" , "ignorant", "judgemental or "stubborn" and end up dismissing someone prematurely.
So before deciding if someone is wrong, take stock of yourself and make sure you're right.
In the words of Carl G. Jung "Everything that irritates us about others can lead us to an understanding of ourselves"
To good health & great relationships.