Not sure what meaningful distinction you think you're making between "carelessness" and "accident" here. The accidental part was him not zipping up his bag. If you're insisting that the only things we're allowed to call "accidents" are those in which no human error occurred at any level, that's a pretty high bar.Why do you say it was an accident?. The OP admitted that the macbook was not secured properly in his backpack, the result being it fell out of the backpack, that's not accidental, that's carelessness. People have a very bad habit of passing things off as being an 'accident' when in fact it is not. This was totatly avoidable.