Bet sizing and opening ranges!
In fact the early stage of MTT when players are deep stack is in fact very similar to cash game. Main difference is that in MTT levels are changing and blinds and antes constantly go up which forces you to play more hands so that you can survive and continue forward. This requires constant change of your playing style depending on the current blinds, effective stacks and proximity to the money zone. MTTs have relatively lower risk as you can only loose your buyin and if you go deep you can earn much more than your buyin. There is also the risk though to play for several hours and at the end with one wrong decision to bust before the money and these hours of play to mean nothing.
In my opinion MTTs require more planning and adaptability and are more prone to variance influence. Cash games can be more profitable if you are really good player and have good bankroll management.
You'll (almost) never be in a spot where you're considering 3bet jamming for your cash game life.
Both require a different kind of patience, MTT's are more dynamic, and require you to adapt to all the different situations you are in, an because of the number of players participating, variation is also higher than a cash game.
In Tournaments, the pressure of the blinds together with our stack in relation to that of the rival, "forces" us to play in one way or another, while in cash we do not have that pressure and the hands are independent of each other.