All of the following are routine. We will name our example person "Bob".
1. Bob owns an important item. He believes that he knows where it is. He is wrong.
2. Bob owns an important item. He is well aware that he has no idea where it is.
3. Bob owns an important item. He knows where it is. He is right about where it is. Unbeknownst to Bob, other people frequently borrow or otherwise meddle with his item.
4. Bob has taken his important item with him, for security. Unbeknownst to Bob, it fell out of his pocket an hour ago.
5. Bob used to own an important item. When he cleaned his house, he confused it with a different, unimportant item, and he threw it away.
This is not something that people are good at.