^^^ Everything Hasrat said, basically.

You 100% can blindly bumble through most general cast and catch big fish if you are determined to, but given some fish can be down for days at a time if they're a weather proc it will be miserable unless you enjoy the experimentation. Fishing is, surprisingly, a very social job and it's how the information is out there for all big fish in the game.

There are a ton of resources online that are community driven for big-fish that help take the guesswork out if you're OK not doing things totally blind, even just the fish tracker that Carbuncle Plushy runs is an immensely useful resource as it tracks time/weather/bait for procs to try hook the fishes, or if certain mooches are needed to chain to that big fish.

Everything else from there is patience (and frustration when you get to Certain Big Fish in SB/ShB/EW, since it's all a game of RNG no matter how prepared you are) and perseverance.