is sitting on it then it produces more friction so it becomes difficult to drag it.
the force required to overcome friction at the instant an object starts moving from rest is a measure of static friction and the force required to keep the object moving with the same speed is a measure of sliding friction.
when the object starts sliding, the contact points on its surface do not get enough time to lock into the contact points on the floor. so the sliding friction is slightly smaller than the static friction.
we would not be able to walk on the surface or floor if there is no friction. it is the friction 