Everything that moves is moved by another.
A moves, therefore A is moved by B
There are three possibilities:
1.A is moved by B, B is moved by C, C is moved by D and …D is moved by A (Circular)
2. A is moved by B, Bis moved by C, C is moved by D, ad infinitum (infinite regress)
3. A is moved by B, B is moved by C and … C is moved by D (the chain terminates)
So 1 cannot hold because the cyclical argument is repugnant.
2 cannot hold because an infinite regress is repugnant.
Therefore 3 must hold. So the chain terminates at some point and we arrive at the unmoved Mover.
Why does this argument fail.
First of all, 1 and 2 although they are repugnant are possible. Gravity supplies the extra energy needed to keep the chain moving.
Secondly, for 3, I don;t see how God can be an unMoved Mover. At every Mass, God responds to the prayers, by coming down to earth and effecting the miracle of Transubstantiation. And God did come down from heaven and was made man 2000 years ago. God responds to our prayers. So God is not unmoved.