Karma vs just bad luck

IMO..Our lives are not predestind as the Christian dogma believes... we are in charge of our own destiny. If we harm someone yes it will come back to us... but it does not apply to everything that happens in our lives. For example... I have a very old car... I know it will break down from time to time... is it Karma that it breaks down after I have a disagreement with someone... or is it just that the car is old and falling apart? IMO.. it has nothing to do with Karma, bad things happen to good people all the time. I have yet to meet anyone who doesn't have challenges to overcome in their lives.

But what do you think? Do you believe everything has to do with Karma?