I mean I understand how it can happen.
The cop asks for id, while getting it he says I have a gun. Officer then has a split second to process 'gun' and says 'don't reach for it', philando says 'I'm not' but maybe still goes for id, cop says 'don't reach for it' twice more then starts firing.
1) Officer should have said, 'put your hands on the wheel' or in general should not have been so reved up after being informed by the dude that he had a gun.
2) While philando should have kept his hands the wheel while telling the officer, I dont feel like this is super important. If you live in a society that allows guns to be carried around you need to have social protocols that are slack enough to let a 1 second miscommunication not end in someone dying.
3) The officer made a decision to takes someones life rather than risk his own even a bit and in this situation with this video this is very up setting, he could have waited half a second more and no one would have died. I don't think I'm wrong in expecting better of an officer and thinking that they should be more accepting of the risks of their job. There also needs to be consequences for failure to preform when it results in a death other than being out of a job.
4) This just contributes to the larger theme that cops will not be persecuted by juries, which erodes the whole belief that people can come to the state to get justice. This is on top of actually getting evidence that cops might have done something wrong and on top of just getting cops to be on trial in the first place. If this happened on its own its a tragedy, but with everything else its a stacked system in favour of police.
5) This happened due to a system of racism and gun culture. If he was white i bet this wouldn't have happened. If every officer wasn't thinking everyone could have a handgun, this wouldn't have happened.