Discernment vs. Letting Go

Anyone who really knows me knows that I'm a thinker. In fact, the majority of them would say I'm an over-thinker. That may be true. I don't like to think of myself that way. I like to think of it as me trying to be smarter and to figure things in life out- why they happen, what I can do to change or grow, what I need to do to protect myself, what I need to do to allow God to mold me, etc. But the problem I seem to have is that when I constantly think of all the things I think about, a lot of times I don't get anywhere. Sure, I think of all kinds of new things, all kinds of possibilities, all kinds of answers which lead to more questions. But as far as finding peace and satisfaction in an answer, well that rarely happens. Naturally, I thought about it (haha) and I've inferred that the problem has to do with Discernment. I want to have discernment, which is most of the reason why I think about everything all the time. But where is the line drawn between trying to figure something out and having discernment? What I mean is, sometimes I'll try to figure things out so hard that I think of all the "what if's" and I try to make sense of everything and I do it because I want to be wise. I don't want to make the same mistakes and if I can prevent something in the future by understanding something now, I want to. But many times these thought processes just go round and round and don't seem to help. So how do you know when to let an issue "be" or to truly seek it out and ponder it?