Once upon a time there was a tricycle. In theory it was a tricycle; however, two wheels had been lost, so its rider struggle along on one wheel.
Now, some skilled people can ride a unicycle well, but a tricycle should not exist with a mere single wheel. Those in charge of parts promised to start looking for more wheels, but there were not a lot of wheels available.
Eventually another wheel joined the trike, and things rode better. The parts people said they would look for a third wheel, but the tricycle functioned pretty well.
Riding a two-wheeled-tricycle tires the rider out, and it stresses the trike. After a while, a wheel began squeaking. Those in charge of parts promised the wheel that a third one would be found soon, but they had to fix other parts first. The rider kept struggling along.
Eventually, the squeaky wheel fell off the trike. Now the parts people panicked because they needed two new wheels. The rider had to struggle in unicycle mode again, and things just were not pretty for anyone. The parts people realized it might have been better to find a third wheel earlier, even though the tricycle had still been moving along.