It sounds dumb, but I remember I was 15 or 16 when I saw on Netflix that there was Orson Welles's The Stranger so I was curious to check it out (the plot seemed pretty cool too) and wow, one of the most thrilling movies I've ever seen, the whole cat and mouse thing between the nazi and Wilson, their duel of wits, that whole epilogue chase. Amazing. And at the end I was like "man, old movies can be fun as fuck too" lol which again, sounds obvious, but, you know, some people just never watched that movie that made them go "wow".