They exist dependent on change. And all of us here exist dependent on change. The breath goes out then it must come in. It must have this change. There must be both the in breath and the out breath.
Sensations are the same.
There must be these things. If there is no wrong there can be no right. You must be right first before you can see what is wrong, and you must understand the wrong first to be right. This is how things are. For the really earnest student, the more sensations the better.