forget, forget about

[Lenka]

I've always thought that the verb to forget directly collocates with its object (better said, the object collocates with it directly).

forget sth.:
E.g. Don't forget it!
I have forgotten buying the book. (X I've forgotten to buy the book.)

Anyway, I have read collocation "forget about sth." today. When do you use it? What is the difference between the verbs to forget and to forget about?

forget about sth.:
E.g. They ought to forget about the unpleasant experience. => is it possible to replace it with the "bare" form of "forget"?

[Tdol]

'Forget about' can have the idea of not thinking about something, rather than having no memory, so they shouldn't dwell on the unpleasant experience and should push it back in their minds.