In any event, in any device, in any change, some human needs to be responsible for it. When it comes to my car, that someone can't just be me. When it comes to my sister, it can't be her. It's that simple.
True, wrong, wrong.
I would certainly trust myself with working on a car/plane/boat that I have MY ass in/on rather than anybody else. No one in the whole world does have a better reason to take special care than I do in this case and as an "amateur" I can spend the time and have an extra deep look at everything in general or a thing that has raised my suspicion in one way or another.
And I have certainly seen dangerously bad jobs done on cars by those "professionals"...