Is it possible for you to see white blood cells with the naked eye? why?

Yes: There is a phenomenon of vision termed entoprics or the flying corpuscle vision which allows viewing white cells. You need to look at a clear blue sky, or a light colored uniform painted all and sort of defocus your eyes. After a monent you will see a dance of translucent objects just outside the center of the vision. Each of this is a white cell traversing the central capillaries.