The goal is clear direct individual tetrads to their respective places and know that their descent is never-ending. You see, the game of Tetris is the game of life a series of neverending, largely conquerable tasks. In Tetris, there is no such thing as the unexpected. Tetrads come in seven shapes. You will never encounter another form.
Tetrads always stick to their meek and humble ways.
My tetrad pals also descend in an orderly fashion. They never yell obscenities from buildings under construction or go to open mics and make bad music. They don't wiggle from side to side, smile, dance or stop. Their speed changes, yes, but it is with absolute reason and consistency. One never fears a sudden downpour.