> [Tetris] simply shuffles a list of all 7 pieces, gives those to you in shuffled order, then shuffles them again to make a new list once it’s exhausted.

Interesting tidbit! So all the times I've furiously cursed at my gameboy because I swear the 'I' is by far the rarest tetrimino and it hasn't given me one for at least 20 turns... was just classic cognitive bias.