For the sinful nature desires what is contrary to the Spirit, and the Spirit what is contrary to the sinful nature. They are in conflict with each other, so that you do not do what you want.
The Spirit is working at that which pleases and glorifies God. It is out for ultimate joy. But the sinful nature is short-sighted. It is seeking after the temporary pleasures, that do not last.
And we end up at war within ourselves.
Most of you know exactly what I am talking about.