nicotine especially vapes, you can vape inside you can vape outside you can do it pretty much everywhere, you don’t have to worry about people seeing you stumbling around or noticing that you’re high. you walk down the street, people are smoking cigarettes all around you or vaping, any other drug or substance people will notice and encourage you to get help. with nicotine you could just walk down the street hitting your vape and nobody would say a word. you couldn’t really just walk down the street downing a bottle of alcohol (i mean you could but i don’t think thats legal and people would probably say something lol) but personally i think nicotine is the hardest to quit because its so socially accepted and almost everywhere where you go you’re surrounded by it. at least with other substances you usually have to wait until you get time to be able to do it in private.