"A profound unmitigated loneliness is the only truth of life"
- R.K. Narayan

But how will it be happy in such a small space?

Okay, make the cage bigger then.

But as it gets bigger, it gets heavier. How will it move the cage around?

Okay, giving limbs to the cage - two hands, two legs. Now the cage can move itself around.

But still, it's so dark inside the cage, and the air stinks.

Fine! making two holes in it - let's call them eyes, they'll let the light stream in. And two more called nostrils, for inlet and outlet of air. Now you would say it's so silent inside? That's taken care too. I gave the cage two ears too! Happy?

I don't know. What if the cage feels small someday, and there is a desire for an even bigger one.
Okay, here's making the cage to grow over time. Every day it keeps growing and gets bigger.

But still... what if?

Go on! I am not angry. You can ask!

What if the bird does not want the cage at all and just wants out?

That, my friend, is a choice for the bird to make. It's not for us to decide. We are just cage-builders.