The spare tire is round, making it easy to roll.

The more humble than the spare tire is the jack—used only when changing a tire.
The most humble is the tripod, constantly reminding others not to hurt it.
And the accelerator keeps fueling people every day, yet is stepped on beneath their feet.
The windshield shields him from wind and rain, but in his eyes, it’s just transparent.
The rearview mirror isn’t afraid of wind and sun, never been looked at directly.
The air conditioner warms and cools, but he only sees it as air.
The seatbelt hugs him every day, but he only holds the steering wheel.
Even more humble is the airbag; it stays safe and never deploys, but when he’s in danger, it sacrifices itself to protect him.
But at least they are in the car, while you, friend, may not even get on the car.