Example I've heard: buying all the tubes of a certain kind of paint in an art supply store in anticipation of doing some huge project. The project realistically would've taken years to complete & their delusion was they were an unnaturally fast artist. Once they snapped out of it, they realized the work they'd done so quickly was shoddy, at best, though they couldn't tell in the grips of mania. They returned most of the unopened paint the next day.