The left side of my face

Why did I have the presumption that I use the left side of my face/tongue /throat/ eye the same way I used my right side? When I attempt to write with my left hand I usually give up fairly quickly and say 'forgetaboutit'. It is not that it cannot write with the left hand. I know how to shape the letters but badly. My left hand participates in typing without thinking about it now but it was difficult in the beginning.  Why did I think I was using the left side of my head in a way that was equal to the right. It is clear to me that I do not. Not that it can't.