Wet boards and dry boards
The rule
A board is wet when many hands improve on the next card, and dry when almost nothing does.
Two cards of a suit and three in sequence is a board where a large share of the deck changes who is winning. Ace, seven, two rainbow is a board where almost no card does. The strength of a hand has not changed between them, but how long that strength will last has.
This is why the same top pair is worth protecting on one board and worth slowing down with on the other. On a dry board the hands that could draw out mostly do not exist. On a wet board they are half of what somebody is calling with.
Read more: outs, implied odds