Why does the same key do something different?

A key’s action depends on which screen is open. These are the ones people mix up most:

Key	In the library	Elsewhere
M	Enter / exit Lens	Info in preview; keep both in Duel.
O	Clear the decision	End a scene in preview.
Enter	Rename; choose the opponent if there’s a Duel candidate	Add an item in Search; decide in comparison; save in frame mode or text.
Space	Open preview	Close preview; play/pause in Duel.
Backspace	Clear the decision	Go to the parent folder in Import; undo the last item in an empty search box.
← / →	Move between clips	Step through frames in frame mode; move one second in the timeline; choose a side in comparison.
⇧ + arrow	Add to the selection	Step through frames in preview; step through seconds in frame mode.
L	All filters	Play / speed up when a player is visible.
1–9	Add to a folder; create a folder for an unused number	An unused number does nothing in preview; 1 / 2 runs a search in the G menu.

If a key doesn’t do what you expect, first check which window is open. Then check whether you’re in a text field. Leave the field and try the shortcut again.

Quick flow: watch with Space → decide with 1–9 / F / R → undo with ⌘Z if needed.