The next rule is this: don't work for worthless things, and don't work uselessly. Don't chase what you can't get. And don't spend years struggling for something, only to realize too late that you wanted the wrong thing. Make sure your effort leads somewhere. And make sure that destination is worth the journey. Most sadness comes from one of two places: either you failed to get what you wanted, or you got it and then felt ashamed of wanting it in the first place.
The next point to these will be to take care that we do not labour for what is vain, or labour in vain: that is to say, neither to desire what we are not able to obtain, nor yet, having obtained our desire too late, and after much toil to discover the folly of our wishes: in other words, that our labour may not be without result, and that the result may not be unworthy of our labour: for as a rule sadness arises from one of these two things, either from want of success or from being ashamed of having succeeded.