I've been towing gliders in an Ag Wagon (C-188) since early spring... have been making an average of 50 landings in it per week for the last 4 months or so. On my last landing of the day last weekend I came closer to ground looping than I ever have before in my 200+ hours of tail wheel time. Honestly, it was probably the worst landing I've made since I was a student pilot. Luckily I recovered, everything was fine, and the most important part, there were no witnesses.

The lesson is you're never good enough to not mess up. Fatigue and overconfidence were both factors I think.