If two people go out for the night, one of them drinks 20 pints, the other drinks 0, on average, they've had 10 pints each.
More generally, this isn't a Corbyn issue. It's a left issue. We believe in facts, evidence, reason... so few of our leaders ever do simple relatable soundbites well.
A boss, a worker and an immigrant sit at a table with 12 cookies. The boss takes 11 cookies. He says to the worker, "careful, that immigrant wants your cookie".