What Am I?

This is a poem riddle. See if you can guess the answer!

What am I?

What am I?

I’m with everyone you meet

Taken for granted by most

Then, for some,
I almost leave them,
And they share their stories to others
How my almost-departure has “enlightened” them
They now appreciate me
To the fullest

Some value me too much
Afraid to take any risk at all
Their paranoia spreading like what it is:
A plague.
Any risk
Any risk at all
And I will leave
–That is what they believe

Some value me
For other reasons
Another plague
This time, of greed
They value me in themselves,
But not in others.
They don’t even bother to think
Where else I could be
But in them
Only in them
Their constant thought—“Me, me, me!”

Others think about me
Try to appreciate me
But
Sometimes,
They forget.
I leave someone else,
Someone they know,
And—BAM!
They remember me again
Try hard to appreciate me to the fullest…
Again…

What am I?