When someone has lived his entire life being needy and seeking validation he can't be told to stop being needy and behave in a non need way. It's weird and a simple change of mindset doesn't cut it for a lot of guys. We've been invested in what other think of us for too long. It's comfortable, it goes with the flow we have some friends, we get by. So it's hard to stop being that way, we don't always want to change. But what I've found is that if you start with non-needy actions you'll learn how to lose your neediness. For example, you're at the college cafeteria, many tables are occupied but there are only a few people in the cafeteria. Why? Because everyone decides to take their own goddamn table, including that cute girl you saw when you walked in. You get your food and look around for an empty seat, but as you do that you catch a glimpse of that cute girl sitting alone. The thought of sitting next to her and talking to her crosses your mind for a half-second but you're not actually down to do it. Why? Because she might be creeped out, people might look at you and think you're weird, the conversation might go poorly and you might get shot down, etc and all the other bullshit you tell yourself. The point is, you only act in a way that you feel will be ok with other people. You need that validation because you're so unsure of anything you do. That is neediness. And I'm not sure for everyone, but it was at least this way for me. One does not simply stop being needy. The way I see to remedy this is to jump the gun, and change your actions to be non-needy to develop a non-needy mindset rather than change your mind-set to develop non-needy actions. Go talk to that cute girl sitting alone 20 feet away from you. Just ignore all the voices in your head for a second, disregard what anyone could say about the interaction you're going to have. It's gonna feel really weird, every fiber indoor body is going to try to stop you from doing it. But just do it, have the interaction. And whether you cared about the outcome of the interaction at the time or not, after it you will realize that doing things for yourself because you want to is exhilarating. And it feels a lot better than the status quo no matter how bad things go, you do it for yourself and answer to no one for it. And that's not needy. That's fucking sexy.

tl;dr: My advice is that if you're having trouble adopting a non-needy mentality, stop thinking too much and focus on non-needy actions and you will develop the mindset. Focus on doing things for nothing and no one else other than your own will. And whenever you catch yourself being hesitant to act in a way you want, just go for it, this is all for you in the end.