Why the Big Blind's range often gets stronger on the turn

It's a mistake to assume high cards on the turn are good for the player who continuation bet on the flop.

A mistake I see often is players who assume high cards coming on the turn are good for the preflop aggressor and bad for the preflop defender (usually the Big Blind).

Most thinking players have a simplified heuristic that low to medium cards tend to be better for the preflop defender, and high cards are good for the preflop aggressor. Which is true...on the flop.

This changes on the turn, however, depending on the flop action.

There is a big difference between when it goes check/check, compared to when it goes check/bet/call.

Have they thrown away their junk? 

When it goes check/check, the defending player keeps all their low cards in their range. So any low card coming on the turn is good for them.

When the flop goes check/bet/call, you can expect the defender to throw away all their low cards that haven't hit. When it is a spot where the aggressor is supposed to c-bet a lot, the defender will often continue with high cards.

Typically, the defender's range gets much stronger on the turn when it goes check/bet/call because they have thrown away all their junk.

As such, high cards are often very good cards for them. It's a mistake to see an Ace or a King on the turn and automatically assume it's good for the player who made the continuation bet.

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