Ok, this is the explanation for League of Legends. I don't know what Einstein meant about that, though.
In League of Legends standard game (consists of 5 players per team; there are two teams), a player can choose one of the three lanes where he will go initially. They are the top, middle (mid) and bottom lanes. Therefore, the mid pertains to the middle lane, where there is usually one player going there. There are two players for the top and for the bottom.
Feeding means being killed by an enemy champion (or enemy player). You are feeding the enemy because he gets gold (money) from killing you.
"Mid or feed!" will always be an "option", but a very bad one. It
basically ensures your teammates that you're an idiot and will most
likely just feed anyways, no matter if you go mid or top or support...
Besides, this basically destroys any possibility of teamwork right
from the start, during champion selection, and the obvious consequence
is a flat quantity of reports.