With 13 tiles and exactly one away from “4 melds + 1 pair”, your hand is ready (also known by the Japanese-derived term tenpai); the tile(s) that complete it are your winning tiles. Ready = sprint mode: now you either draw the tile yourself or wait for someone to discard into your win.
Example: what is this hand waiting on?
Look at the 13 tiles below. The 3-4 of Characters is a connected partial run — either neighbor could complete it. Think for five seconds before checking:
Answer: the 2 or the 5 of Characters (a two-sided wait). Draw the 2 and 2-3-4 forms a run; draw the 5 and 3-4-5 does — both roads lead to a win.
How to find your winning tiles
The method is “fix, then flex”: set completed runs and triplets aside — they won't change — and study the partial shapes that remain. Two consecutive tiles (like 3-4) wait on both neighbors; two tiles with a gap (like 4-6) wait only on the middle; a lone tile waits for its pair; two pairs each wait to become a triplet. Fluency here is playing strength — it's worth drilling specifically.
Self-draw and deal-in
Self-draw: you draw your own winning tile — all three opponents pay you, the best outcome. Deal-in: another player discards your winning tile and you call it — only that player pays. Which is why strong players watch the table: late in a round, discarding a tile someone might be waiting on is dangerous.