Lots of people talk about bicycle tire rolling resistance but I don't think that very many folks understand it.

When you sit on your bicycle a portion of your tire flattens against the ground. As you ride, that flat portion is constantly moved to a different section of the tire. Take a bare tire and try to flatten a section of it with your fingers. You can do it easily enough, but it obviously takes some effort. As the bike rolls along that effort ultimately has to come from the rider. Old hard tires are always going to be harder to bend. Tires with thick puncture resistant belts are always going to be harder to bend. Thin, supple tires are always going to be easier to bend but will cut or puncture more easily.

To a point, inflating your tires harder will reduce the size of the flat spot and, since you have to bend them less, the rolling resistance of the tire. Exceeding that point, however, will make your whole bike bounce upward over every tiny little pebble in the road. The energy that's required to lift the bike and rider also has to ultimately come from the rider.