Board must allow a low

You need three low cards on board to combine with two from hand (2+3). Board K-Q-J-9-9 → no low possible. Don't chase lows that can't get there.

A2 is key and duplicated multiway. Bare A2 without backup is playable but dangerous — prepare to get quartered.

Low needs five unpaired cards 8 or under using exactly two from your hand. No low → high scoops the lot.