set in
phrasal verb with set verb uk/set/ us/set/ setting | set
（不好的事）到来，开始（而且可能会持续）
When something unpleasant sets in, it begins and seems likely to continue in a serious way.
This rain looks as if it has set in for the rest of the day. 看来今天雨不会停。
If you get bitten by a dog, you have to make sure the wound is cleaned well, or an infection could set in. 如果你被狗咬了，必须确保伤口彻底清理干净，否则可能会发生感染。
Despair seems to have set in among the team. 整支队伍似乎都陷入了绝望之中。