Ok, this is a pretty basic question, and I’m sure I’ve simply missed the explicit text in the book which discusses this, but here goes…
For example, let’s say I’ve earned 3 checks in a session, but due to circumstances, I simply can’t come up with a use for one of them at the end of the session. (Say, another player wanted to do exactly what I’d planned for my last check, I don’t have any conditions, and I’m all out of other ideas.)