Estimating your opponent’s poker hands
Being able to figure out what kind of poker hand your opponent has is the difference between winning and losing in poker. You usually make a guess based on previous behavior, how much aggression your opponent has shown so far, the position your opponent is in (acting first is a huge disadvantage) and so on.
If you make no estimate what kind of poker hand your opponent has, you can only reason in three ways:
a) You assume he always has the best poker hand. So you throw away your hand.
b) You assume he always has the worst hand. So you put your chips in.
c) You bet big if you have good cards, and you throw your cards away when your cards are lousy.
Clearly (a) and (b) are bad strategies.
The last strategy is not as bad as the other two, but still terrible. More often than not your cards are bad. So your opponent will figure out you’re not willing to make large bets with lousy cards, so every time you don’t bet, he will, and every time you bet, he won’t. You’re going to lose your chips that way. This is basic game theory.
So you need to figure out what cards he could have been dealt so that his actions make sense. Then, from that range of plausible cards, figure out how often he has a better hand than you do. If you like your odds, you put your chips in. Otherwise, you throw your cards away.
It’s a lot more complex than this, of course. But the point is that “estimating your opponent’s hands”, as difficult as it may be, is absolutely crucial if you want to win.