I have had one total engine failure, crank broke on takoff and one partial, very rough engine due to mag failure on 1 and partial on 2, despite both showing good on engine run up 2 hours earlier. The first time I just got away with it, the second was more relaxed as I was only loosing about 50ftm. That is in 950 hours. Both problems were traced to faulty parts and maintenance. Moral of tail, take a big interest in the maintenance of your engine and it is much less likely to fail on you.
Rod1