Was usually careful when the roads first got wet due to oil on the road mixed with water is pretty slippery. One day I didn't slow down to go over a couple sets of wet railroad tracks . Hit them about 50 or so and started fish tailing right off. Made it about 70 or so yards before going down.
Guess I lucked out, in all the miles I rode I never got surprised by the road surface in front of me. As pointed out, first rain-slick roads after it hadn’t rained in a while were the worst, ‘specially at intersections. In the rain what I would do to test traction would be to touch a foot to the ground while moving.
An often overlooked dangerous scenario is topping a rise in a straight road that lulls you into riding faster than you can see. A buddy did that and found himself passing through a herd of cows at 80mph, the head of one knocking a hard luggage piece off of the side of his Beemer My own one hard wreck that I had was after topping a rise at 90 to find a poorly-marked 30mph turn.
I came across a sudden dip in a Hill Country backroad onetime only to find it filled with floodwaters from a thrunderstorm cell upstream, the road otherwise bone-dry where I was. 80 when I saw the water, got on the brake, 60 when I actually hit about 50 yards of water 1ft deep. I knew enough not to touch the brakes. Hit the water with a tremendous RRRRIPP!!!! sound, big wave. Fortunately I was on my KLR - tall and narrow. Even so the front end shimmied and the bow wave knocked my feet off of the pegs. On a regular road bike I would have hydroplaned and gone down.
Topping a rise early on in my riding career changed my braking habits forever. Came over a rise at night to find a deer broadside in my lane. Tunnel vision and slow motion arrived. I recall the front tire howling like they do when about to lose traction in hard braking. Then that deer just ran in slow motion out of my field of vision and I let off the brakes.
I wasn’t aware of it but in braking so hard I had locked up the back tire and the back end had slid to one side. When I got off the brakes the bike snapped back straight and I ended up sitting on the gas tank, weaving wildly. Was able to recover.
After that I used only my front brake when it was dry, running the front tire to the edge of losing traction is something you do instinctively, only a total newbie locks up the front wheel when it’s dry (hard to do on dry pavement anyway).
Conversely, on wet roads I would use only the back brake under normal circumstances. Now of course 90% of your braking power resides up front, the back brake always sucks, so in the rain I would adjust my riding habits accordingly.
Worked for me.
"...if the gentlemen of Virginia shall send us a dozen of their sons, we would take great care in their education, instruct them in all we know, and make men of them." Canasatego 1744
My own one hard wreck that I had was after topping a rise at 90 to find a poorly-marked 30mph turn.