Hard puzzles expect pairs and triples as a matter of course, and every so often force an X-Wing — a pattern where a digit's candidates in two rows line up in the same two columns, letting you eliminate it from those columns everywhere else. There's no guessing at any point; the pattern is always there to find, it just takes a slower, more deliberate scan than Easy or Medium ever demanded.
Want to ease up? Medium is a step down. Ready to go further? Expert is a step up.