On the one hand, Schopenhauer’s advice seems perfectly sensible—accept what you cannot change, choose your battles wisely, don’t put yourself into situations where the patience required overreaches your own capacities. But on the other hand, it might seem that his pessimism about the fixity of character—that is, his unflinching determinism—is ultimately self-defeating. If character is fixed and all is determined, then what’s the point of offering advice? It’s tempting to think that the advice must be either futile or unnecessary. If I am hopelessly impatient, then the advice is futile, since impatience is an unalterable fact about my character. If I am patient, then the advice is unnecessary. But if the advice works, then doesn’t that show that character isn’t fixed? That is, if I take Schopenhauer’s advice to heart, practice being patient first with inanimate objects and then with other people, and if I thereby become more patient than I have been in the past, then doesn’t my own growth in patience disprove his claim that character is unalterable?
A determinist like Schopenhauer could respond in at least two different ways. First, he might argue that the advice is still good advice even if some people are incapable of following it. Patient acceptance of what cannot be otherwise is a necessary part of coping with life. Some people find life unbearable because they are deeply impatient rather than because they’re really that badly off. That’s too bad for them. Their example makes clear the advantages of patience. But second, Schopenhauer can also argue that the truth of determinism doesn’t imply that advice has no point. Advice itself can serve as a cause. A person might have the capacity to be more patient than he has been in the past, but there must be something that activates (or triggers) that capacity. Schopenhauer’s Counsels and Maxims might turn out to be just the thing I needed to see how important and useful patience is, and to see at the same time that I have the ability to be more patient than I have been. Or perhaps reading Schopenhauer will stimulate me to recognize the limits of my own patience, and cause me to limit my own exposure to situations that I can expect to require more patience than I have. I wouldn’t become more patient in that way, but perhaps my life would go better in virtue of living within the limitations of my own lack of that virtue. So it’s not true that his advice is pointless; rather, its effectiveness (or lack thereof in some cases) is simply subject to the same causal laws that govern everything in the universe. This will be little consolation to the hopelessly impatient, but there’s nothing to be done about that. And it’s hard to imagine someone who is hopelessly impatient taking the time to read Schopenhauer anyhow!
These possible responses might raise questions about what it could then mean for Schopenhauer to claim that character is fixed. Perhaps that for any given person, only a certain amount of flexibility and growth is possible? A more pessimistic view would be that people can’t change or grow in any significant way, but it would be difficult to know how exactly to vindicate such a universal claim. It may be true that we tend to settle into our ways, that, for the most part, you can’t teach an old dog new tricks, but tendencies aren’t universals, and even radical changes seem to be compatible with the general truth of determinism. (A radical change would simply require a radical, or unusual, cause.) Whether it is compatible with Schopenhauer or not, perhaps a realistic outlook would involve being mindful that we are at risk of fooling ourselves if we start thinking that we just happen to be exceptions to general rules of human nature and psychology. We should aspire to patience, but also be mindful of the possible limitations of our own capacities, and try to avoid setting ourselves up for the failure and frustration of testing our own patience beyond its limits. Of course, if determinism is true, then we ultimately do whatever we do. We succeed or we fail. We repeat past mistakes or we learn from them and grow. But since we aren’t omniscient, the truth of determinism doesn’t itself provide any practical guidance: we don’t know what our own deterministic future holds. So, at the practical level, the best we can do is to try to do the best we can do. The best Schopenhauer can do is to advise us to accept patiently what cannot be changed. Life may be pointless, but if so, then there’s no point in being miserable about it. (See his "The Emptiness of Existence.")
[Reassuring, I know. But here I'm mainly just trying to work out a reading of Schopenhauer's advice with an eye toward moving to some extent past it. Thoughts on the middle paragraph above are especially welcome!]