I've had to break these out more than I would have liked recently, but they're a great tool in the proverbial box when you need them.
I simply put them on when the weather is being less than cooperative, then repeat to myself one of the following cheerful affirmations and proceed on my ride:
"It's actually kind of bright out."
"I think it's clearing up."
"It's only a sprinkle."
"It's really just a light mist, mostly."
"It's not raining, that's just marine layer."