If an upsetting thought pops up just when you are about to sleep, and you don’t recognize that the thought is making you unhappy – and the mind starts chewing on that thought – you start thinking and thinking and cannot sleep. You don’t recognize that it’s an unwholesome thought and it shouldn’t be entertained.

The unwholesome thoughts, they are well practiced and they know what to do; but for us, either we don’t know that we need to stop it, or we can’t even stop it if we try.