We riding bycicle, when tyre pressure is low we fell riding is hard. Why?

Please anyone tell the actual answer!
Thanks Rudi_in, for posting your answer to the Ask Me Help Desk. Please answer also this question.

More rolling resistance when the tires are soft.

Did you mean FEEL riding is hard? Then the answer is as Need said, the lower the pressure, the more tire contacts the road, the more rolling resistance.