I remember having an interesting discussion with an old Jesuit priest in which I wondered whether a number of venial sins committed could ever add up to being as bad as one mortal sin. He said an emphatic no. I tested him: ten, fifty, a hundred, a thousand? He stuck to his beliefs – no, mortal was mortal, it deprived one of Divine Grace, venial could never be the same. I was not so sure.
I also recall chatting with a friend about the theory/fable of the frog in boiling water: put a frog in a pot of water and very gradually heat the water. The frog will not protest even as it boils to death. I said I doubted this – there would come a time when the frog realizes it was in grave danger and would flop about and try to jump out the water. My friend said – absolutely not so. We never did put a frog through a practical trial.