If you want to clue somebody into something that is happening, you give them the heads up. If you think that somebody is clueless, you may say that they have their head up their ass. If you think that somebody has their head up their ass, you may want to give them the heads up. That is the Buddha’s message in a nutshell. Heads up.
If your head were really up your ass, you would have a unique perspective of yourself. You would also suffer. If somebody pointed out to you that your head was stuck up your ass, you probably wouldn’t believe them and you may become angry. Two symptoms of having your head up your ass are not knowing exactly where your head is, and becoming easily angered. If somebody told you that the way to end your suffering was to take your head out of your ass, and you began to entertain the idea that your head may actually be up your ass, then you would probably do all you could to change your head space.
The Buddha’s message is more compassionate and less vulgar, but it is essentially a heads up to the idea that there is a way to end your suffering. One of the roots of suffering is a sense of a separate self. If you see the world with your head up your ass and you recognize where your head is, then you will also realize that everything you see is you. When you notice that all you are seeing is you, you no longer feel so separate from it and your suffering stops.
Your head is always up to something that causes you to suffer. Whenever you notice that you’re suffering, just give yourself the heads up and realize that your ass is perfect.