Many people truly have this difficulty called toothbrush abrasion. When you brush too much, you damage your teeth and gums. When this happens, you develop sensitive teeth and gums that recede.
Thus, people who take too much care of their teeth are in trouble. About 10% to 20% of people brush too much because they think too much about oral care and they use brushes with hard or medium bristles.
If you brush too fast, at least go for soft bristles.
Do not be fooled by any commercials saying medium or hard bristles are fine. They can damage your gums and cause wear on the root portion of your teeth.
Do not brush aggressively.