Can someone explain to me how you lose (and then find) a satellite?

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Can someone explain to me how you lose (and then find) a satellite?
https://www.washingtonpost.com/news/inspired-life/wp/2018/02/01/this-amateur-astronomer-found-a-satellite-lost-in-space/

Since the thing is orbiting earth, why can't NASA just look up in the sky
with a telescope to find it?

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