In a disk brake setup (which is what this Tesla has) there is a caliper with slots for two brake pads on each wheel. So with 4 wheels that would be 8 break pads

In a disk brake setup (which is what this Tesla has) there is a caliper with slots for two brake pads on each wheel. So with 4 wheels that would be 8 break pads. The caliper squeezes the pads on both sides of the rotor (which is turns with the wheel) in order to slow down. This is why having one left over (or just an odd number left over) is a red flag. You can’t put two many in, there is no reasonable way to make that mistake, but you could leave one out, so it makes sense to check for that mistake.