From memory of the times (although not directly involved), there were two beliefs current among bomber crews:
(a) if you (or, to be exact, your pilot) survived your (his) first five 'ops', you had a good chance of getting through the next 25 (the "infant mortality" theory).
(b) As losses averaged (say) 3% per night, and the roulette wheel has no memory, your chance of survival each time were 97%, and remained the same on your last trip as on the first.
It was my good fortune to be shipped out East of Suez, where most people came back unless they were either unlucky, careless or stupid, and the foregoing considerations did not apply.
D.