Someone can send you bitcoin without asking you, and it can be a fortune. It raises another concern, that if it is a mistaken sending, will you keep it or return it to the sender in such case, it depends on you.
Depends on the reason it was sent.. I expect such person to initiate another transaction utilizing script like
nulldata script (OP_RETURN) stating whatever was the reason for sending such fortune to my address(either it’s a mistake or not).
I know someone might ask what if the person doesn’t know how? The thing is losing such fortune will force you to find a alternative toward reaching out to such address, else without an attempt.. it could have a lot of meaning to the receiver..