Some carpets are in rougher shape than others. Carpet is soft to the touch and can be damaged or worn very easily. Down here in Tampa FL we have a real problem with sand aggressively scratching carpet fibers and wearing them down prematurely. When I tell people they have sand in there carpet they're surprised because they can't imagine where its coming from. Especially, if they have a no shoe policy in their home. The thing is the fine sand here in Tampa FL is going to find a way into your house. You dig down 6 inches in most areas you'll find sand.
The best thing you can do for your carpet is vacuum twice a week to get as much sand out as possible. Then every 6 to 12 months have a professional carpet cleaning service come in and clean your carpets. Carpet cleaning can remove the majority of fine sand and slow down the wear and tear on your carpet.
If you have pets in your home I recommend having your carpets cleaned every six months. One pet can bring in as much sand as a family of five. Their paws trap sand between the pads and track it into the house. Consider vacuuming 3 times a week if you have pets.