Before the events of Dragon Ball, in Age 461, Master Mutaito sealed the Demon King Piccolo in a rice cooker with the use of a move called the Mafuba. The Demon King's reign ended and world peace was restored, but it came at the cost of Mutaito's life. From there, his two pupils Master Roshi and Master Shen parted ways, set up rival martial arts schools, and decades later imparted Mutaito's teachings onto a new generation of pupils.
... Except for the Mafuba, otherwise known as the Evil Containment Wave in the Funimation dub. In fact, when Emperor Pilaf freed Piccolo from his culinary confinement and the world was threatened once more, Roshi was adamant that Tien Shinhan not learn the technique, taking matters into his own hands. Roshi uses the technique on Piccolo, but fails and loses his life, prompting Tien to learn the technique against the late Turtle Hermit's wishes.
However, when Tien unsuccessfully attempts the technique against the Demon King, he emerges unscathed. The reason for this remains a mystery, as it's not like the Mafuba has to be successful to take the user's life - after all, Roshi died in spite of its failure. To manga author Akira Toriyama's credit, the aforementioned scene is only present in the anime, with Tien never getting an opportunity to use it in the manga. What's less excusable is the next time the move is used in the manga, where Kami attempts to trap Piccolo Jr., only for the Demon King's heir to reverse the move and seal Kami instead. Neither Jr. nor Kami dies as a result of their use of the move, definitively putting an end to the death rule.
It makes sense that the Z Warriors would be reluctant to use a move that guarantees the user's demise, but since that's not the case, why don't they use it in future battles? Had the Z Warriors taken a pair of rice cookers with them to the battlefield, the fight against Vegeta and Nappa would have been over in a matter of seconds. The same goes for Frieza, Cell and Buu -- even in the direst of straits, nobody brings the move up as an option.
It takes until Dragon Ball Super for the move to come up again. In the Goku Black saga, Trunks tries (and fails) to seal the immortal foe Zamasu with it. In the next saga, the Universe Survival arc, Master Roshi uses the Mafuba against multiple opponents in the Tournament of Power, successfully knocking out Universe 4's Dercori. It's in this arc that the risk of death comes up for the first time since its initial use. While one use isn't enough to kill Roshi, Krillin fears that constant use will eventually take his master's life again. By Roshi's third attempt, it's clear that the Turtle Hermit is at death's door.
This suggests that it could be strength that determines the user's resistance to the technique's strain. While it's hard to quantify Roshi's strength during the Tournament of Power, it's fair to say that he's substantially stronger than he was during the battle against King Piccolo. Super's loose power scaling means it's hard to work out exactly how much stronger the characters are compared to Z, so perhaps characters only recently reached a point of being able to withstand the death drawback -- although why Kami survived in Dragon Ball remains a mystery.
Of course, there are other explanations. The fact of the matter is, these characters are martial artists who battle not just to protect the universe, but also to measure their abilities. To Goku and friends, there's no appeal in using a move that wins matches for you by default. Super shows that there are circumstances where that's not the case, such as with Zamasu where there was simply no other way to win, but otherwise, our heroes would rather win on their own merits. Moreover, the technique doesn't exactly have a stellar success rate -- only Mutaito's use against Piccolo and Roshi's use against Dercori definitively worked.
On a more meta-level, it's possible that Toriyama simply realized his mistake in introducing an instant-win move so early into the story. The Mafuba debuts in chapter 135 of Dragon Ball, just over a quarter of the way through the manga's original run. The characters having a technique that guarantees victory in their back pocket would undercut a lot of the drama of later arcs, so Toriyama potentially quietly dropped the move in the hopes that the audience would forget that Frieza's reign of terror could so easily end at the hands of a humble kitchen appliance.
The Mafuba is a popular technique among fans for a good reason. The death drawback makes for an interesting dilemma for the characters, it gives the often-neglected Master Roshi a use in the story, the rice cooker gag is funny and the move just plain looks cool. However, there are also good reasons why it's only used sparingly. It's to the Mafuba's credit that despite its failings, it's as beloved by fans as it is. Let's hope that the next time it appears in the story, Goku and co. have a little more success with it.
