I'm going to use an example here. I like the ability + skills = how good at something you are system. Here's why. Let's say I want to be a meat-head. Good. But I want a meat-head who can crack into computers but only has an int of 9. To overcome his smart deficiency he can dedicate some of his training to cracking computers. Will he be good at doing other brainy things? No. But he can at least crack into a computer. It keeps the whole, anybody can learn anything, but not everybody can learn everything. The same could be said for the nerd who practices his jump skill... a lot. And that's all he does.