3 wheels and their point of contact define a plane with the floor and are enough to create a stable rolling shopping cart, yet every shopping cart has 4 wheels, and the 4th one is nearly always spinning wildly if you look at all of them while pushing. This is a result of fabrication and wear. Even if manufacturing could hold tolerances tight enough to keep all the wheel in an even level plane, eventually the wheels get bent, or wear down from the asphalt outside.
Yet no one stops making 4 wheeled carts. Even if they cost more than necessary. Even if they don’t provide anything better than a 3 wheeled cart would.
The world is filled with problems like this. Problems that don’t make sense to tackle because no one is suffering as a result of fixing it. No one sees this as being a defining problem that will allow them to break into a new industry. Basically, there isn’t much incentive to solve this kind of problem.
Which means that if you are into problem solving, it’s best to make sure the problem you’re solving, isn’t in the same category as making a 3 wheeled shopping cart. Make sure it’s valuable and worth your time.