Position

You open the button with A-10 suited and only the big blind calls. Flop: 9-6-2 rainbow. She has to act first, and she checks. You've seen that check before you've spent a chip, so you bet half the pot with ace-high and a backdoor straight draw and take it down. She had to decide blind and hope; you got to answer her with the last word on the street. The check told you she had nothing, and the bet cost you almost nothing to find out.

That edge is worth real money over thousands of hands. In position you value bet thinner, because you can see whether a scare card actually changed anything before you commit. You bluff more, because a check hands you the weakness you need. Out of position you're guessing — check and give a free card, or bet into a raise you never saw coming. It's why the button plays more hands at a profit than any other seat: the chair is worth chips before you look down at your cards.

The beginner mistake is treating a hand's strength as fixed no matter where you sit. K-9 offsuit is a fold under the gun and a fine steal from the button. Same two cards. The value moves because the number of players left to act, and how much you'll know on later streets, both change with the seat.