NL Preflop Question

[cwsiggy]

I've always been curious how one figures all this math out in the heat of the moment. I can understand putting people on hands and knowing if you are a favorite, but all the EV weighted calcs seem a lot harder to do a the table. Does one get better as situations repeat???? Do yo study common structured hand problems and as the closest ones come up say "oh that's that one" - fold
Someone enlighten me.