As far as my insecurities are concerned, they are ALL related to not being wanted. I deal with thoughts of "if I was bigger, better,...blah, blah, blah". Other HDM here have indicated they have the same thoughts, so I guess it's common. That doesn't really help, though.
I'll add on some thoughts here. I truly believe all men worry about size. I have some strong preferences.... but must say that really hard is what does it for me. Sometimes, men have made comments about not being very well endowed. Most of the time they have been somewhat accurate in their assessment.
Bear with me while I'm extremely technical and realistic about this. I can touch my cervix-- without fully inserting my finger. I can touch my tounsils equally easily. This means that anything as long as my finger, well, frankly is long enough. Girth/thickness is another issue, and there, a finger is not sufficient
You can also do amazing things with adjusting positions for depth, fullness if size is a realistic (versus imaginary) issue. All that said, I know that it's hard to not feel wanted, and when that's the case, it's natural to try and figure out the "if onlys". I've thought if only my breasts were bigger, my hips were smaller, I tried a Brazilian, etc etc..... but deep down know that none of it matters when the important stuff is okay.
Never try to teach a pig to sing. It wastes your time, and annoys the pig.