On our Happiness by Baruch Spinoza

Now that we have seen the advantages of this True Belief, we shall endeavor to fulfill the promise we have made, namely, to inquire whether through the knowledge which we already have (as to what is good, what is evil, what truth is, and what falsity is, and what, in general, the uses of all these are), whether, I say, we can thereby attain to our well-being, namely, the Love of God (which we have remarked to be our supreme happiness), and also in what way we can free ourselves from the passions which we have judged to be bad.

To begin with the consideration of the last, namely, of the liberation from the passions, I say that, if we suppose that they have no other causes than those which we have assigned to them, then, provided only we use our understanding aright, as we can do very easily (now that we have a criterion of truth and falsity), we shall never fall into them.