Why quadruple bonds are not likely for a carbon atom? (Please explain in terms of pi/sigma bonds or hybridization)

I understand that the first bond between two carbon atoms is a sigma bond then the next bonds are pi bonds, but why can't the 4th bond be a sigma bond? or i'm just messing everything up?

Can someone explain this to me properly? thanks

Question

Why quadruple bonds are not likely for a carbon atom? (Please explain in terms of pi/sigma bonds or hybridization) 

I understand that the first bond between two carbon atoms is a sigma bond then the next bonds are pi bonds, but why can't the 4th bond be a sigma bond? or i'm just messing everything up?

Can someone explain this to me properly? thanks

aaronq · Answer

the orbital (geometrical) orientations don't allow for these bonds to occur.