What's the hardest part of controlling two Tetris boards at once?

I'm the solo dev behind TwoGrid Blocks, launching Tuesday. The core mechanic: you control two Tetris grids simultaneously — one thumb per board, both dropping at the same rate.

Building it, I discovered the hardest design challenge isn't the code — it's tuning the difficulty curve so both boards feel equally demanding. The moment one side gets harder, your brain locks onto it and abandons the other.

From my playtesting, there are three distinct cognitive barriers:

1. **The initial confusion** — first 60 seconds where you can't coordinate at all

2. **The false confidence** — around level 3 where it feels manageable, then speed ramps up

3. **The click moment** — when players suddenly manage both grids independently (usually 5-10 minutes in)

Classic Tetris players actually struggle more initially — muscle memory from single-board play actively fights against dual-board thinking.

What do you think would be the hardest part for you? Would love to hear what cognitive tricks people use to manage split attention tasks.