A one-day hike in the Black Mountains in Ireland a few summers ago (with my teenage son, a same-age friend of his, and my SO). We had an arrangement with the travel agency for a 3 day hike from B&B to B&B: they took care of the luggage, gave us the documentation (including maps and instructions) and booked the B&Bs. We had a 6 hour hike that day, and left at 10am. Then it started raining a little, then it started really pouring, and it poured on and on. My balance is not very good, there were bits with mud and clumps of grass, other bits with very unstable rocks, up or down, depending, so I was in constant dread of falling and breaking something. It was a nightmare. Everything was slippery and sloped. There was no stopping the hike - we were in the middle of it, it was either go back or go forth, equally bad. We were soaked through and through after 2 hours, and I fell a lot (without breaking or spraining anything, thankfully). The 6 hour hike turned into a 9 hour one, and I have never been more relieved than when we finally arrived at the B&B. I couldn't eat anything that evening (and that's after 9 hours of walking), I was under the physical shock of it.
When I asked the specialized travel agency why they haven't warned us of the rain forecast (we were at the departure B&B till 10am, after all), they said that they hadn't had time - right . When I asked them why they hadn't mentioned a walking stick in their (extensive) list of things to take with us, they said oh yeah, maybe that would be a good idea. I gave an earful about them with my Swiss travel agency, who had subcontracted them for that part of a bigger Ireland trip.