Why some guys are nervous or afraid to approach women they like?

The reason why some guys are afraid to approach women they like is because of lack of self-confidence, they think they don't have the skills to approach them. But why do they think so?

1. Low self-esteem and self-worth: Someone who developed low self-esteem/self-worth will often overestimate girls worth and underestimate his own worth. He may think a girl is out of his league despite he and her come from the same social class, because past life experiences shaped his identity and make him developed low self-esteem over the years based on what he believes people think of him. Any attempt to act outside this identity or misconceptions he developed trigger the same feelings you experience for example if you attempt to touch ember or bare electric wires (see causes of shyness and lack of confidence for more details). If you are afraid to approach women because you think they are out of your league despite both of you are from the same social class, chances are your fear is based on how past life experiences shaped your beliefs and conditioned you to think that way but not because they are out of your league.
2. Fear of humiliation: They witnessed the instances of how girls publicly humiliated some guys for asking them out, and from there they formed the belief that girls treat guys who approach them with disdain.
3. Fear of embarrassment: They witnessed some cases where someone asked a girl for a date but she rejected him and all people around laughed at him
4. They once asked a girl out but she rejected them that's why they think any other girl will do the same.
5. Lack of social skills: Whenever you have something, there is possibility that you missed something else. People who focus on their career or study are less likely to go for dating, if you spend most of your time on study or on financial achievements, chances are you missed developing social skills. If you lack social skills you also lack confidence. Social skills is necessary if you want to success in dating. And social skill is an independent skill that need to be learn.
6. Halo effect: Halo effect is a cognitive bias whereby our perception of someone influences how we feel and think of him/her. Research shows halo effect influences our perceptions of attractive people. Men unconsciously overestimate attractive girls, they think because they are beautiful they also possessed positive traits as well and their life is perfect so they are out of their league because they may already have many boyfriends.
7. Horn effect: Horn effect also is a cognitive bias in which people underestimate someone based on one negative trait. If someone has one negative trait, chances are people will underestimate and put him down, overtime he will feel inferior and developed low self-esteem and whenever he saw a girl he likes he will instantly overestimate her values and underestimate his self-worth and this will make him afraid to approach her for fear of rejection.
8. Fear of rejection: The overall reason some guys afraid to approach girls/women they like is fear of rejection. Almost all guys will never have any problem approaching women they like if they are 100% sure they'll get accepted, but because most of them are not sure of their acceptance, that's why they are afraid to approach women for fear of rejection because rejection hurts. Rejection is hurt because unconsciously you feel you are rejected because you have some faults or because you are not worthy enough.

Dating is like sports, you can only get good at it with practice. Without practice you'll never progress. There is nothing wrong with asking a girl out or being rejected by a girl, being rejected doesn't mean there is anything wrong with you, but an indication that you're not her type. Each of us view the world differently because we have different unsatisfied needs, values and have different life experiences, as result of this we find someone attractive but not others. Just as men are very choosy when it comes to girl physical appearance, women too have their own preferences.