Why does a new toothbrush hurt?

Brother, it's not a new problem, it's that your toothbrush bristles are too hard. My gums are very sensitive, and I dare not have any bristles. I bleed when I brush. Later, I changed to Panasonic's EW-DM7 1 electric toothbrush, and the hair was very fine. It feels completely different, completely painless and very comfortable. And the vibration is divided into light and heavy files, depending on the bearing capacity of my teeth. I started with soft gear, and slowly I used heavy gear.