lol my dad used to be a heavy smoker, but due to his health issue, he literally quit like right after he took his x ray showing that he got pneumonia. He never touch 1 cigarette after that, nor did he ever crave for it :'>
I think it's only possible to quit right after if a person knows that there's already a imminent threat to that person's health but for people who are in their early 20's (or younger) who still look (and thinks they're) healthy but smokes frequently, it's hard since they still don't feel the effect of their vices in their body and thinks that it is still okay
Anyway, I hope your fathers health is back in good condition already.
Smut aside, in reality, it really is hard to quit smoking. Like, you cannot just give up everything within a day. Most of the advice I heard from smokers who were successful in quitting said that it is much better to take less and less as the day goes by and at the same time look for another healthier alternative.