What is invalidation level?

Every trade thesis makes a claim about the market, and every claim has a price that would disprove it. If you buy because a support level is holding, the invalidation level is a clean break below that support.

Defining invalidation before entry is step two of the Decision Protocol. It gives the stop loss a reason to be where it is, and it gives position sizing the distance it needs.

A trade with no invalidation level has no exit for being wrong, so it tends to become a long-term hold by accident.