What can someone else have for you, and give to you, without it ever becoming yours?

Something that many of us can name long before we know the first thing about its nature. Something you can receive constantly for years, yet you may never have any, nor really even know what it is, until you find you have some that's not for you—but instead for someone else; often for someone whose you've never expected yourself to have, and still might not. When you have it for anyone else, it's always yours, that you still have no matter whom you give it to.

What can go unseen by those to whom it is shown, and often remains unknown to they whom it is made for?

It's the most difficult thing in the world to show to those who don't know what it looks like( but think they do), even though they most need to see it; most difficult to give to those who don't have it and most need it, even though you won't lose it and most people want to receive it.

The thing most important to keep showing & giving; even to those who might never see it nor have any for themselves, let alone have any to show or give to you & others.

(Hints in the comments.)