The modern lifestyle is a mostly sedentary one with most people spending more time on their backside than on their feet. All this sitting with little or no exercise is doing a lot of harm to the body and can affect the health negatively.
Basically, sitting is a normal human body posture, and when people work, socialise, study or travel, they often do so in a seated position. It’s second nature.
However, it’s the amount of sitting that’s the problem as it can be harmful if you do too much of it. And these days, our lifestyles encourage most people to sit more.