Riding a bicycle is an unnatural activity.
Riding a bicycle should not hurt.
Pleasure, comfort, efficiency, endurance, and performance come in choosing a bicycle to fit, adjusting a bicycle to fit better, and training to better use a bicycle.
A bicycle is like a pair of shoes. If it fits well, you don’t notice and can go all day. If it fits poorly, you notice.
Many people ride on bikes too small with the saddle too low. Some ride with the saddle too high. Many ride with the handlebar too low.
How you fit a bike changes with time.