I find it difficult to motivate myself to
start a ride in the rain, but will do it on forum rides, audax rides and sportives.
It is much easier going out on a day where rain is not forecast until much later in the ride. I'll do that and put up with the rain. It's usually not too bad as long as you are dressed for it.
I have done a few rides where the weather turned ridiculously nasty and I chose to cut them short. When the rain is so intense and cold that the roads start flooding and hypothermia becomes a real possibility then there is no joy in it, and I adopt the motto 'discretion is the better part of valour', go home, and live to ride another day!