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I have just started learning Japanese Mahjong and I am a bit lost as to why this hand failed.

I did several pons and chis over the course of a hand, having a total of three open melds (one set and two sequences).

Apart from these I had an incomplete bamboo sequence of II and III as well as a pair of dragons, therefore I was on a single wait for I or IV bamboo stick tile. When the IV tile appeared in one of the discards of other players, I was given a choice to do another chi and declare another open meld, but I couldn't win with a ron. Why was that?

Am I wrong that winning by ron guarantees a single needed yaku to win a hand, just like Closed Tsumo does?

After declaring the chi I was offered with, my hand was left with a single pair of tiles, one of which I had to discard.

Eventually the round finished with a draw.

Why couldn't I win this hand with a ron on the IV bamboo tile, and why was I given only the choice of chi instead?

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Calling ron does not give you a yaku. What it will do is increase the fu count of your hand, but only if the hand is closed. However, winning from a ron on an open hand does not increase the point value at all; contrarily, you could instead claim a 2-fu bonus by winning on a tsumo.

Once your hand is opened, the only way to win is to have a yaku that does not rely on a closed hand. Opening your hand before you have a guaranteed yaku, or a good chance of building one, is often a mistake; not only does keeping your hand closed increase the number of yaku you can potentially make (especially "easy" yaku such as pinfu and tanyao), but you also have the option of adding the needed yaku just by calling riichi on an otherwise worthless hand.

If you do decide to open your hand, some common open-hand yaku which can be built follow:

  • Yakuhai: A complete set (not pair) of dragons, seat wind, or table wind.
  • Chanta: Every set contains either honor tiles, or at least one terminal (1 or 9) tile.
  • Itsu: Three melds "123", "456", "789" of a single suit.
  • Honitsu: All tiles, except for honor tiles, comprise a single suit.
  • Toitoi: Every set is either three or four of a kind (i.e. no chi melds)

Some rulesets also allow a yaku for an open tanyao (no honors or terminal tiles). There are of course others, but I find these listed above are typically the easiest to make on an open hand, especially if you open early.

Even if you can't memorize all of the yaku-bearing hands yet, it's worth it to at least memorize these ones for when you choose to go the open-hand route.

That said, given the (incomplete) description of your hand, your best bet would've been to wait for a third dragon so as to claim a yakuhai yaku, and hoping to complete a pair involving one of your two bamboo tiles (while tossing the other). Calling chi on the bamboo actually harmed your hand, since you no longer had any reliable way to form any yaku.

Not knowing the makeup of your open melds, I don't know if calling chi on a I Bamboo (instead of a IV Bamboo) would've completed a chanta (or possibly an itsu) hand; even if it was possible, it would still be a risky wait as passing on the IV Bamboo (while waiting on the I Bamboo) would put you into furiten.

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  • Thank you! I must have misinterpreted the rules and somehow I was sure, that with an open hand I can't call tsumo without apparent yakus, but I can win with a ron. You have clarified this to me perfectly - now I understand. Thanks!
    – Mateusz Papiernik
    Commented Sep 26, 2012 at 12:00
  • It may sometimes be useful to open your hand as the wall shrinks, even if you won't meet the yaku limit, simply to ensure your hand is in tenpai. This nets you points on an exhaustive draw. A partially open hand in temporary furiten (by passing on a completing tile) can call a meld that would be a duplicate to end the temporary furiten (instead of waiting for a turn to pass). As well as that, some rule sets will provide yaku for "events" rather than hands - for example, winning on the last draw/discard of the round.
    – Samthere
    Commented Sep 26, 2012 at 14:54
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I found this page that explicitly states the problem in the OP.

Essentially, certain properties of the hand give multipliers (yaku [役]). At least one multiplier is necessary for the hand to win.

Multiplier, or "fan", is based on properties of the hand or how it was won (yaku). For instance, a fully concealed hand (menzenchin tsumohou [門前清模和]) gives 1 yaku, so the win condition is satisfied. In the example given in the OP, no multipliers apply. For a list of multiplier sources, see here.

Other common sources of yaku include:

  • fanpai [翻牌] / yakuhai [役牌] - "Pon of honors" - A tri or a quad in any element / the round or position wind.
  • tanyaochuu [断幺] - "No Terminals" - A hand with no terminals/honors. (Sometimes required to be closed though - this depends on the actual rules in effect)
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The OP may have confused Ron with Riichi. If you declare Riichi (hand is in Tenpai - one tile from completion), then stealing the last tile with Ron satisfies a Yaku. But it is the declaration of Riichi that is the Yaku in this situation, and not the final Ron call.

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