Nothing Is Happening with my ring doorbell motion detector....

A friend parked in front of house my and walked up my steps and nothing was recorded and no alerts sounded. On my ring doorbell 2. What up, why did this not happen? There was Nothing matter of fact, it went to black. I did all the motion checks and balances this for my front door ring2 this has also happened with my rear doorbell too. But, let car go by there is motion unless it's my neighbors coming the cars appear out of nowhere. Please advise.