Complacency
Last spring I discovered that a small exhaust leak had worsened, removed the exhaust and got it repaired by a very good welding shop, (permit aircraft) replaced it and continued to fly through the summer. Two weeks ago the battery wouldn't start the thing so to get flying I swung the prop. An hour later it started no bother. Three days later had to swing it again, I put this down to cold weather, so, removed the battery to recharge it. Discovered a hole two inches dia melted through the underside of the battery casing exposing the plates, no acid left, bone dry. The battery tray is about half inch above the exhaust, I'm surprised it held a charge all summer. Next in the line of fire, literally , is the fuel filter/gas collator/fuel pipe work.
I am not inclined to dwell on "what if" scenarios so I'm not about to lose any sleep over it. However I certainly learned a lesson, don't be complacent just because it's a lovely day to fly and we don't get many at this time of year.