Back to the World of Existentialism...

In his work, "Existentialism is a Humanism," Sartre adamantly states, "there is no reality except in action...Man is nothing else than his plan; he exists only to the extent that he fulfills himself; he is, therefore, nothing else than the ensemble of his acts, nothing else than his life" (pg. 654). Do you agree with Sartre? Are we humans only determined by our acts and not by our thoughts or feelings? Sartre seems to place a great deal of emphasis on physical action, as suggested by this quote, but perhaps this is a misinterpretation? However, if this is not a misinterpretation, what would Satre say of some one who had felt that he should be a world-class musician but found that he could not perform on par with other world-class musicians and was a mediocre musician at best? That is, would he think that he was not reaching his full potential and was falling short of achieving the greatness he was capable of achieving? If a person is really the sums of his actions, it would seem to follow that any action that is taken or not taken to achieve one's end would not constitute a full life, in the eyes of Sartre. Aside from the quote, I do have one other question left with regard to Sartre's piece, "Existentialism is Humanism": Sartre seems to place a heavy emphasis on the suffering of man. In fact, he calls man "anguish" because he is thrown quite literally into a world where he has to endure not only his suffering but others' suffering as well. If indeed the world is full of suffering and man is really anguish encapsulated in flesh and bones, why does any of this matter considering existentialists do not believe in an after life? In other words, if there is no hope for an after life, then why would an existentialist claim to feel such suffering for his fellow man if he knows that all is futile and will end in its time? Why not make the most of what life has to offer with as much pleasure as possible?