Check out the link that TFOX posted, That explains it better than I ever could. This is as useful for hunting as it is target archery. In the case of tree stand hunting, even more so as you will be shooting at extreme angles.

The site will show you that it is normal for the arrow to be coming out at a different angle as your sight picture at rest. I might warn you also to not overthink the issue unless you want to excercise you brain a little more.