I'm looking at all sorts of guides for characters and a lot of them say something along the lines of, "If the enemy team has one of the following champions, do not pick this champion" and then lists a bunch of champions that can act as hard counters against the champion in question. For instance, this AP Yi build I'm following states that I should not pick AP Yi if I encounter squishy mid-laners and/or squishy support on the enemy team, but how would I possibly know that? The characters need presets like Masteries and Runes to get their full potential out, so if you pick your runes and masteries for a certain build, going another will be detrimental.
How would anyone possibly know what the other team is going as? Do they get shown before the match begins, before even the loading screen, in ranked matches? In regular queue matches, I cannot possibly know if the other team has any champion that these guides are telling me to pick a different champion if I face them.