[ethan_g]

Certainly the first thing that's apparent when watching pros play is their speed. However, after playing years of Tetris myself (though nowhere near pro level), I've really come to appeciate that speed is only a small fraction of what makes pros pro.

* Many multiplayer games give bonuses for combos (multiple consecutive line clears), T-spins, and Tetrises. Setting these up efficiently can require reading several pieces ahead and takes a ton of practice. An example where both players do a fairly elaborate setup, one with combos and the other with T-spins: https://www.youtube.com/watch?v=mASSHXLTuU4

* 20G mode, made famous by games like TGM, drastically reduces the ability to manipulate the pieces. Even surviving takes new strategies (you're forced to play a lot of strange moves), much less making tetrises like the pros do. https://www.youtube.com/watch?v=aoU0DQh7zdU

* Some multiplayer games give difficult garbage, I'm thinking of Cultris 2 specifically. Clearing garbage efficiently, known as "downstacking", requires much more careful piece placement than regular play. It's hard to appreciate from video, but if you compare pros downstacking to a normal person, you can see they use fewer pieces to clear the same amount of garbage, which is a real competitive advantage. https://www.youtube.com/watch?v=OgK4aJ_3zCw