  The payoff matrix highlights the fact that weak altruism is individually advantageous, and thus the oddity of thinking of it it as altruistic rather than selfish. To see this, assume for a moment that the game is being played by two rational agents, as in classical game theory. Clearly, the rational strategy for each individual is W, for W dominates N. Each individual gets a higher payoff from playing W than N, irrespective of what its opponent  does—30 rather than 20 if the opponent plays W, 10 rather than 0 if the opponent plays N. This captures a clear sense in which weak altruism is individually advantageous.