Why do some ideas come like a wave and others trickle in like a stream?

Some of my best story ideas came to me like Venus on a half clam shell emerging from the ocean, that is, fully formed. Within half an hour I had the plot, characters, setting, even sometimes the ending.

Others trickle in bit by bit, or never fully emerge. I’ve had one story plot trick for 20 years and have never figured out what to do with it. (I’m not sharing in case some day I do!)

Meanwhile, my hard drive fills with fragments. Lucky for me it’s just electrons and not pages, or I’d be out buying a bigger filing cabinet.