They can ephemeral but potentially sticky, pervasive, and annoying.
Thoughts are like magnets. We can't turn them off. We're always thinking about something.
Try to go a minute without thinking about a white bear. It's impossible. Thoughts lead us right into the thing we're trying to avoid, even that pot hole.
Thoughts depend on the chaotic connectivity of neurons. But the chaos is why it all works.
We can meditate and try to inculcate certain thought patterns like positivity. But the process is mostly futile. Controlling thoughts is exactly what gives them strength.