Some people say birds should be free. They think birds should fly around on their own will. "Vast opportunities mean greatness." they say.
What about the bird that doesn't fit in with the rest, the one that does not fly with the flock.
Imagine being thrown into a room crowded with unfamiliar people, how does it feel? Now imagine a bird is in a mindset where the future is endless, but it's feeble mind cannot possibly fathom where it must go.
There is no straight path, so it stays in place. Now, if one puts a cage around thyself, the brass object with bars gives a sense of security. There are not a billion choices the bird can stay put.