Taiji and Steel

I just had a piece of thought on Taiji.

Taiji is considered strong, why?

A large plate of steel is also considered strong too (structurely), but it can't hit you by itself.

If you try to punch at it, your knuckle will probably hurt quite a bit.

If someone tries to push onto a Taiji practitioner with a high level of skill, that person should feel having a great force come right back at him. I think that part of the Taiji training is to make me seem like a solid wall, and force directing at me can "bounce" right back at the source.