Our Identity and Actions

Does who we are determine our actions, or does our actions determine who we are? Quoth Jean-Paul Sartre:

Certainly we cannot say that this man [a young student of Sartre’s who in 1940 had to choose between going to England to join the Free French Forces or staying in occupied France to care for his mother, who depended on him], in choosing to remain with his mother — that is, in taking sentiment, personal devotion and concrete charity as his moral foundations — would be making an irresponsible choice, nor could we do so if he preferred the sacrifice of going away to England. Man makes himself; he is not found ready-made; he makes himself by the choice of his morality, and he cannot but choose a morality, such is the pressure of circumstance upon him. We define man only relation to his commitments; it is therefore absurd to reproach us for irresponsibility in our choice.