Answer:
I have one, you have one. If you remove the first letter, a bit remains. If you remove the second, bit still remains. If you remove the third, it still remains.
There is an ancient invention. Still used in some parts of the world today. That allows people to see through walls.
I am a good state, there can be no doubt of itΝΎ But those who are in, entirely are out of it.
I can run but not walk. Wherever I go, thought follows close behind.
At night I come without being fetched. By day I am lost without being stolen.
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.