Blind battle (SB vs BTN)

It folds around to you in the small blind (SB) and the button opened. Only the BB is left behind. You have 3 options: re-raise (3-bet), call, or fold.

Here you play out of position (you act first on every street) and the BB can still wake up and squeeze you. That's why the SB plays mostly 3-bet or fold: you call very few hands. You re-raise your strong hands for value and bluff with some suited hands; everything else goes in the muck.