でカップのをと、お湯を入れるにをだけ開けます。飲みたいので、全部はがしたくなることもあります。でも、を開けると、が少なくなって、手がすべりやすいです。
When people buy cup miso soup at a convenience store, they open the lid only a little before pouring in hot water. They may feel like peeling it all the way off because they want to drink it quickly. But if they open it too wide, there is less place to hold, and their hand can slip more easily.
とくにお湯ののでは、片手にスマホやを持っていることもあります。が残っていると、上からのも逃げやすくて、あとで閉じてこともできます。全部取ってしまうと、机まで運ぶあいだに中がすぎて、こぼれそうにるもいます。
Especially in front of the hot-water machine, they may be holding a phone or a rice ball in the other hand. If part of the lid stays on, steam can escape more easily and they can close it lightly again to wait a moment. If they remove it completely, some people feel it may spill while they carry it to a table.
だから、先に線のところまで開けて、その形のままお湯を入れるがです。長く話ではありません。入れたあとにを軽く戻せる形かどうかだけ見れば十分です。
That is why many people open it only to the line first and pour the water in with that shape. It is not about waiting a long time. It is enough to check whether the lid can still be set back lightly after pouring.