If I am on the bike and have no other option than to continue on the bike to get somewhere, I must ride in the rain. Barring hypothermia concerns, once I'm soaked through, its rather meh, and I generally forget the discomfort within a few min. Even if there are clouds impending when I leave, there is always the chance that it won't rain. Thought I was going to get soaked this afternoon, was waiting for it, but it never came. Had I not gone, I would have been PO'd at myself for wasting what turned out to be a good afternoon.

If I am at home and comfy, my options are to sit home or go out in the already failing rain. Not likely that willfully getting wet is going to win that.

Same reason that I have to jump into cold water, instead of tiptoeing in. If you know it is coming, it is far worse than it just happening.