Sudden discovery that OCaml doesn't have just a `==` operator (identity), but also a `=` operator (equality).
That bug took longer to solve than I care to admit and all it was about was incorrect string comparison.
If someone tells you that you'll "pick it up as you go" and to "not spend too much time reading through basics" when you're dropped into a project in an unfamiliar programming language, whack'm. Whack'm hard.