this is no way to work

How does a person, who is non confrontational, an introvert, and with a strong work ethic, go about telling his boss that they just have too much work to do, too much being expected of them? What should he do instead of looking up from his chair each time someone from another department comes into his cube with another pile of things to do. At this point all he can bring himself to do is nod, say he’ll do his best, and try not to show a look of total bewilderment and overwhelmedness that lurks in the shadow of his eyes. And why does his boss not stick up for him? He is also non confrontational. He tells him to just do what he can and the rest isn’t on him. But it is on him, wouldn’t you agree? To the people around him, with no words from his boss, it just looks like he isn’t getting things done and no explanation is offered. What should he do? I have plenty of unsolicited advice for him, but I don’t know if I would even follow my own advice. Should he not rely on his boss and just tell this person and that person that he can’t get such and such done by that date, would this date work instead? Should he stay late every day, becoming bitter and hateful about his job and his work place? Should he say to his boss, look, I know you’ve said I can only do what I can do, but it would be really helpful if you could set some parameters for people in other departments. Should he just take it upon himself to make guidelines for the rest of us and post them on his wall? Something like, If you need thing A done, I need a week. If you need thing B, I need two weeks. Etc.?? I understand we run on schedules and timelines and deadlines here. We have unexpected projects that we just need yesterday. I am one of the people that gives the poor girl so much work. But we are just people, we are human, we all have jobs, projects, bosses, stress, deadlines. Do we all have understanding, compassion, flexibility? What can we do in this situation? Should I be doing something? Should I be an advocate when no one else is? And if so, how? Oh dear. Why do we have to work to live?