Meaning of 無くし in Japanese

I immediately lost my concentration.

It was unfortunate that he lost his passport.

She was in trouble because she lost her passport.

He was fortunate to find the book he had lost.

His name is mud.

He is always losing his umbrella.

My goodness! I have lost the car keys.

I lost my ticket. What should I do?

I don't understand how in the world they can take your stuff for safekeeping, but then the post office guy has the nerve to tell you "Sorry, we lost it" and expect that to be the end of it.

Don't lose confidence, Mike.