Toitoi
Toitoi is a yaku that beginners especially love.
But precisely because people love it so much, there are many cases where they overdo it and fail.
This is especially common in online mahjong, where the game pauses whenever a callable tile appears.
That makes it easy to fall into the habit of calling on everything.
I hope this page helps you reexamine how you call.
When You Should Aim for Toitoi
Dora 
For example, have you ever seen someone start calling from a pair like here even though it is not a yakuhai?
This is a classic example of forcing an open hand too hard.
Even if every call succeeds, the result is probably still only a naked tanki wait worth 2600 points.
Middle tiles such as and are not easy to pon, so this kind of hand often collapses halfway through the calling plan.
Kan 
Pon 
If someone riichi'd against a hand like this, would that not be very awkward?
So trying to force Toitoi from only four pairs is reckless.
Example 2
Draw
The kind of hand where you should aim for Toitoi is a hand like Example 2, where the materials for Toitoi are already basically present.
More concretely:
you already have five groups total of triplets and pairs.
That kind of hand should be played directly as Toitoi.
In Example 2, there is no need to wait specifically for to appear before you start moving.
You should actively call on tiles like as well.
Example 3
Dora 
Example 4
Dora
The borderline case is when you have five pairs.
At that point the hand is also one-shanten for Chiitoitsu.
If you force it into Toitoi, it still takes three steps, or two if you assume a tile comes out that you can pon.
In other words, once you pon, you are actually increasing the shanten count by one.
On the other hand, Chiitoitsu is a yaku that tends to take time even from one-shanten to tenpai.
So if your hand is full of tiles that are easy to pon, Toitoi can sometimes end up being faster.
Example 3 is the kind of hand that should be played as Toitoi, and you could even keep Chanta in mind at the same time.
You should call on almost everything except .
By contrast, even if you call in Example 4, the remaining shape is too awkward, so it is better to commit to Chiitoitsu.
Of course, you also need to watch what tiles are already visible on the table.
If even one pair has already become a dead pair because two copies are visible, then you should decisively commit to Chiitoitsu.
What Should You Do with Suuankou One-Shanten?
Example 5
Dora
With a Suuankou one-shanten hand like Example 5, what do you do if someone discards ?
Some players would say to pass on the first copy.
My view is: even the first one should be taken as ponten.
Whether bonus-chip rules are in play matters, of course, but even without them this is still a hand that becomes mangan on tsumo.
If you do not even take tenpai with a hand like this, that feels too soft.
You should only chase Suuankou in situations where the score actually demands it,
for example when you are far behind in last place and need a big comeback.
Do Not Get Too Greedy
Example 6
Pon 
Pon 
With a hand like Example 6, if you draw , of course you can make it into a Toitoi shanpon wait.
And if appears, it is also fine to pon it and make a higher-value Toitoi wait on 
.
Example 7
Pon 
Pon
But in Example 7, even if comes out, you should not pon it.
If you do, the number of winning tiles drops sharply.
And after already calling three groups, it is almost unrealistic to expect the other players to keep discarding the critical manzu tiles into you.
The hand already has enough value as it is.
Once the hand already has sufficient points, continuing to reduce your acceptance just to force Toitoi is simply getting too greedy.
Once the hand is already worth 3900 or more, keep winning the hand as the priority.
Original Japanese page: http://beginners.biz/naki/naki09.html