The cherry on the cake phrase informal
Used to indicate an additional advantage or positive aspect of something that is already regarded positive or useful.
Jack's very happy because he has a chance to participate in the swimming competition. If he wins, it will be the cherry on the cake.
This apartment has all the modern conveniences, and the beautiful view from 60th floor is the cherry on the cake.
There can be good aspects that exist in a bad situation.
To lose the skill or advantage one used to have in the past
To gain an advantage over someone by doing something before them
If you fall for someone's trick the first time then they are at fault.
Are you going to mess with me again? Fool me once, shame on you; fool me twice, shame on me.