A serious examination will reveal that the root cause of all sin is arrogance. By overestimating our own importance, we effectively remove Hashem, even if ever so slightly, from our consciousness so that we can proceed on our desired path. By allowing our hearts to rise, we feel ourselves to be self-sufficient, not needing Hashem's constant supervision and sustenance. The connection between se'or and the evil inclination now becomes clear. Bread is an illusion.
Yeast causes a tiny volume of dough to expand to a remarkable size.
However, the size is deceiving - it is mostly filled with air. Bread may look impressive, but it is really nothing. The yetzer hara works the same way. It convinces a person that he is all important, inflating a person's ego to grand proportions. The yetzer hara and the se'or are indeed one and the same.