You don’t really know a piece until you know it “even when” well.
I can perform it well…
even when I’m tired.
even when I’m sick.
even when my neighbor is missing.
even when it’s a different time of day than I usually perform it.
even when there’s a car alarm going off.
even when my director stops conducting.
The thing is, for a while you don’t know you’ve reached “even when” until one of those eventualities happens. But with time, you learn to recognize “even when” as a state of being, and know to keep practicing until you get there.