The rot sets in informal
Used to talk about a situation which begins to worsen
The rot has set in since the construction projects were all postponed.
I'm sure the rot will set in if you won't stop.
Used when there are too many people involved in a task, and this can lead to a failure or its likely outcome isn't good
To know and understand a situation only when it has already happened
Used to say that somebody is in a better or worse situation.
The verb “set" should be conjugated according to its tense.
The noun "rot" may have a Scandinavian origin, which appeared in the early 14th century. The phrasal verb "set in" is used when something unpleasant begins and seems likely to continue in a serious way.
If a person has the devil's own luck, he or she has extremely good luck.
A: Yesterday I won a $10 million lottery jackpot and today I won a car in a draw.
B: You have the devil's own luck.