That's not even close to true. Things can work well at first and then stop working after a while. That doesn't mean it didn't work initially.

If we only prescribed pain medication based on your definition, practically none of them would make it through.

Your body adapts to its environment and as such very few things will work in perpetuity.

Bumbing the baby in the cart over a threshold worked very very well initially, for like 3 months, and suddenly stopped working at all.

I feel a great deal of confusion is stemming from that advice might come to late or to early in the childs life.