“I think most people have one top idea in their mind at any given time. That’s the idea their thoughts will drift toward when they’re allowed to drift freely. And this idea will thus tend to get all the benefit of that type of thinking, while others are starved of it. Which means it’s a disaster to let the wrong idea become the top one in your mind.”
-Paul Graham, “The Top Idea In Your Mind.” paulgraham.com. July 2010
If your top ideas are getting money, arguing with someone, the past, how stupid you are and so forth, then your mind is working on destructive bullshit.
cafebedouin.org 
The “top idea” is a variation on how consciousness works: multiple under-the-hood perceptual and cognitive processes compete to gain primacy and enter conscious thought. Stimuli that signal danger automatically rise to the top. Gunfire! Snakes! High-speed vehicle traveling into one’s path. When out of harm’s way, e.g., sitting still and lost in thought, various ideas may spring to mind from among those unconscious processes (most of which are conditioned, since true creativity is infrequent). And most of those thoughts are derived from emotion, not rational thought. Accordingly, many top ideas lack strategic or pragmatic utility. Plus, they tend to loop, self-reinforce, and form habits of mind. Adopting a pose of objectivity/rationality to penetrate the fog and achieve clear thinking, i.e., directing one’s thoughts, is quite difficult for most of us.
Reminds me of that Hume quote:
“We speak not strictly and philosophically when we talk of the combat of passion and of reason. Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them.”
Agree. I think we do get to direct our mind a bit, particularly by not selecting jobs that have us focused on things like money or disputes, such as administration, lawyering, etc.
Also, this is the value of meditation, learning how to not pay attention to thoughts we don’t wish to attend to. Difficult, but it is a skill we can cultivate.