At its core, poker is just a betting game, using cards as a random variable. So, poker is all about math. When calling or making a bet, math determines how profitable you're going to be in the long-run. The problem is, as a poker player, you don't have access to all the numbers. And that's why it's such a challenge.
Having a read on an opponent merely gives you a better assumption of his range, therefore making your math better than someone with no idea what his opponent is holding. But, your math still isn't going to be 100% accurate.
That said, you don't have to be a math whiz to succeed at poker. With so many repeating situations (top pair vs flush draw, for example), experience can make up for a lot of mathematical deficiency. But, an understanding of the math right out of the gates can save a new poker player a lot of time and money.