Think about the specific things you're insecure about: chest/penis size, your nose, your chin, hair, intelligence, etc. Everyone tells you that they're just fine or something else nice about how they really like it that way. You are never convinced though. It's there, and no matter what anyone says, it's your flaw (read this word with as much disgust your inner monologue can manage. It is the verbal equivalent to a naked mole rat puking).
So, what wrong with you? Why can't you just get over it? Simple! You tried to lie to yourself. Maybe your flaw isn't actually a big deal, and maybe some people do prefer what you have over what you wish you had, but that isn't the issue. The issue is that you wish you were different. And it doesn't matter what other people think because you wish you were different. So now you have some options: just be insecure, change it, hide it or accept it.
So first, you could just be insecure. These are women who need constant validation that they are pretty. Most likely, they're slightly above average, but the absolute best looking. They want to be the best looking they want to show all the other really gorgeous women that they can do it too... They can... Just listen, they really can (read this as your inner monologue sobs deeply into a half melted tub of ice cream). I'm men, they become cucks because they see themselves as inadequate, especially if they have a smaller member. Bottom line? Don't be this way. Don't live your life insecure.
So change it, right? If you're a lard-ass, boring nerd, go eat right, start working on your courage, and do things you think are interesting. You'll fix what is a flaw that you don't like about yourself by changing yourself. This is growth. No one wants to deal with a 35 year old toddler, and no one wants to deal with someone who sees changing themselves as something innately super-bad-terriful. I have no issues with this and think you should change what you can.
Oh Gnat! You're so smart and wise, imma go lop off my nose now! Wait, hold up. Now we're getting into the actual point of all this, surgery and cosmetics and even some stylistic changes are not changes, they're concealments. This is metaphysical, though. Plastic surgery gives you a face that isn't yours. Your face is lost forever and you're buying a mask you can't take off. Cosmetics and make up doesn't make your acne, weak eyelashes, and puffy eyes go away. They're still there, just underneath a thin layer of powder. It's a bag over your head and you put a magazine cutout of someone else on. You feel "confident" because you aren't yourself, you're taking a vacation from yourself to act like you're someone else. But you will take the make up off. You will look in the mirror and you will know what you look like, who you are, there will be a subtle, but important difference in what you did while pretending to be someone else, and you'll have nothing to back up yourself with. Now it isn't a completely different person, and it isn't a complete disconnect, but it's there anyway, and I blame most residual insecurities on bad attempts to hide them.
Well what should I do about my lazy eye, huh? Mr. Oh-look-at-me-I-can-be-so-judgemental... That sounded better in my head, but you're a jerk. For the issues and flaws you have that you can't change without truly changing yourself, you have to accept them. Instead of being your flaw, the thing that will always hold you back, it's a flaw, the thing that is simply a part of you. It's still there, you're still bald or have a ruddy face, but that's okay because it's your shiny, basically-a-mirror forehead. It's your beet-red face. Whatever it is, it's yours. It's the reason why I'm so honest with people's appearance. They aren't blind. They can see what everyone else sees, so see it, acknowledge it, embrace it, and move on. And then, accept other people's flaws as well. They have their own issues that makes them some imperfect person. We're all going to make it. But seriously, don't wear make up.