Thinking About Yaku (1)
One of mahjong's pleasures is building yaku.
Anyone is happy when they win with a yakuman, or with a difficult and rare yaku.
Tsumo 
But overcommitting to yaku is also a mistake.
Tsumo 
Dora
For example, in this hand, you should not discard 
just because you can see a possible 234 Sanshoku.
If you draw 
or 
, the Sanshoku falls apart.
And a half-hearted discard like 
is not very good either.
It is better to cut the souzu kanchan and aim for Tanyao plus Pinfu.
Beginners often say they cannot make yaku,
but in reality, more people fail because they chase yaku too hard.
Especially noticeable are players who force their hands toward Honitsu or Toitoi.
It is not rare to see someone call three times and still not be in tenpai.
Mahjong begins with shape first.
First think about how to build four melds and one head,
and only aim at yaku within a range that does not sacrifice too much speed.
There are nearly 40 yaku in mahjong,
but only about one third of them appear often.
You can think of the rest as mostly impractical yaku.
The best example is Suukantsu's smaller cousin, Sankantsu.
Its difficulty and reward are completely out of balance.
Worse still, adding more dora through kans can even turn someone else's simple riichi-only hand into a baiman.
There is absolutely no need to force yourself to chase such a losing yaku.
Let us look at the actual appearance rates of each yaku.
One internet mahjong site, Tenhou, publishes statistics.
| Yaku | Appearance rate | Rank |
|---|---|---|
| Riichi Yakuhai Pinfu Tanyao |
42.6%38.7%22.5%21.2% |
A |
| Honitsu Iipeikou Sanshoku Chiitoitsu Toitoi |
6.1%5.0%4.3%3.0%2.9% |
B |
| Ittsuu Chanta Sanankou Chinitsu |
1.7%1.2%0.8%0.8% |
C |
| Others | Below 0.5% |
D |
(Sample size: over 20,000 hands)
Mahjong has many yaku, but the ones you can actually make often are limited.
What really matters is the skill of building the yaku in this table that are ranked B or above.
Those rare yaku that appear in less than 0.5% of hands can mostly be ignored.
Theory Summary
The difficulty of a yaku and the points it pays are not necessarily balanced.
There is no need to force difficult yaku.
Original Japanese page: http://beginners.biz/teyaku/teyaku01.html