answer:Welcome to Fluther. Your reaction to the missing key was focused on the cost of a replacement and the inconvenience to do so, both of which are, obviously, pretty minor things to worry about. Your mother is concerned with the security issue that is presented by a book bag that was “out of your control” for whatever reason, and for whatever length of time, added to the fact that “now your house key is missing” from the place where it should be, in your bag. Do you see the difference in focus? Her reaction may be somewhat exaggerated and unhelpful – I’m not here to criticize your mother – but it’s not wholly unwarranted. You say that your friend had your bag yesterday, and as far as you know that is true and your friend is completely trustworthy. But perhaps your friend didn’t have control of your bag every minute yesterday, and perhaps your mom doesn’t know – even if the bag was in your friend’s control every minute yesterday when it was out of your control – how trustworthy your friend is.