Friction is the reason humans are able to control where they move or why objects can stay in one place, but it is also the reason we must use force and lose energy to move objects and why many materials wear out and break. The reality of friction allows machines to work, humans to walk and cars to drive. However, friction also means that energy needs to constantly be exerted to move any object.
When two surfaces are in contact, friction stops those surfaces from sliding against each other. All machines make use of friction and without it would have no use. However, friction makes moving large objects extremely difficult and causes surfaces to wear and break. Friction is a physical constraint, but also makes controlled movement and work possible.