The other day I was building something and realized that I hadn't done a trig problem in at least 10 years. I felt pretty sad when I had to look up how to solve it. I still remembered the general concept, but the details were lost on me. Yet, it was important that I knew how to do it.
I'm trying to go through Khan Academy in my spare time to learn and relearn the math that has slid out of my memory.
At least in this case you know what things to look up; imagine never having learned those things in the first place.
I try to quickly learn about every concept I come across to the point that I understand when and why you would want to use it, but not the point that I understand how to implement it. When I encounter a problem that fits the concept, then I can look it up and learn how to do it fully.
I don't know, I feel it has served me well anyway. I like to jump on problems in all kinds of industries, so it is impossible to study everything ahead of time.
You know what is even funnier? That after learning the logic behind programming I was able to perceive mathematical concepts under a whole different view and had so many fulfilling "oh that!" moments so far!