The understanding is always the dupe of the heart.

Reasoning arrives after the wanting and is generally employed by it. You decide somewhere below the level of argument, and then your intelligence assembles the case, which is why the case is always so good. The better your mind, the better the justification it can build for what you had already settled on. That is not a reason to distrust thinking, only to suspect conclusions that happen to suit you.

When you find yourself with a watertight argument for something you wanted anyway, take that as a signal. Ask what evidence would change your mind, and if nothing would, you have discovered that you are not really reasoning about it.