OK, to help visualize....think of the air molecules as a length of anchor chain. Now, visualize a a thruhull (hole) at the bow of your boat. Your task is to get that length of chain through the hole and into the water. Which is going to work better, dropping the anchor and letting it pull the chain through? Or maybe it would be more efficient if you picked up the last link in the chain and tried to push the chain through the hole. Whacha tink, Mon?

Same thing with the air through a radiator...ot trying to herd a chicken.