We must know sensations. Some sensations are pleasant, some are unpleasant, but that's not important. That's just their business. Just like the monkey. We should understand them and know how to let them go.
Sensations are uncertain.
They are Transient, Imperfect and Ownerless. Everything that we perceive is like this. When eyes, ears, nose, tongue, body and mind receive sensations, we know them, just like knowing the monkey. Then we can be at peace. When sensations arise, know them.