We hear or see the stories people warn us of. We take some of them more seriously than others, and from it, choose how to build our defenses. A man who's father often complained about how much money his mother spent, for example, might build much of his defenses around not finding a girl who wanted him for his money.
But no one can defend against everything. There's always a weak, undefended, spot. Fortunately, that undefended spot is usually a spot that isn't of concern - hence why it was undefended. For example, a man who was raised on a farm would never think starvation is a thing that actually happens to anyone, and thus might not build defenses around the idea of a woman using him for his food (if that's even a thing). So, if one day a girl approaches him who intends to do just that, he might even be happy to provide it because it's one of life's easiest pleasures to share that which you have in abundance, with those who have none.
Unfortunately, however, our lack of concern for that weak undefended spot only remains that way as long as it doesn't become calloused. If someone comes along and rubs it too often, you're going to become sore and feeling stupid for not seeing it coming. But that's getting ahead of this story.
These defenses form a mask, of sorts - or perhaps lens is a better word. And like most prescription lenses, it narrows our awareness of the peripheral, whilst also fomenting a dependency on the lens in order to see at all. So to look for the spots you want from others, to see if they are unguarded, you have to look through this lens to see it. You must project your own insecurities onto another person just to see if they have the insecurities you are looking for. But of course they aren't going to just stand there while you examine their weak spots - they're trying to look at yours, too. So, we end up in this odd dance where the two participants circle each other, finding out how sensitive they are in the places they need to be sensitive. This is basically a 69.
However, much like real 69s, this could theoretically lead to awkwardness that can cause relationship issues with gay couples. Men and women each have insecurities that are common for a given gender that they guard, and for the most part the insecurities of men and the insecurities of women compliment each other. But when two people with identical insecurities (or nearly so) try to make it work, they can't flank each other. Like two men trying to give each other blow jobs at the same time, there's no way of doing that without someone choking. Or two women trying to pleasure each other orally at the same time, there's no way of doing that without someone deciding they get bottom. Well, I guess they could lay on their sides, in both cases, and that would fix everything, but I'd imagine it's still awkward because that's slightly less comfortable. But for a straight couple the man is always on bottom, and doesn't get choked by the woman on top - at least in theory.
I'm not entirely sure if I had any point to any of this. I just wanted to draw attention to the apparent fact that no one really gets used for the things they are prepared to not get used for. It's always something out of nowhere. Or something they saw coming but didn't quite understand the scope of the devastation that would follow. But that's how we learn where to put up new defenses.
Also here's an image. I don't know why we need an image, but it said to add one. Okay, then...