Quote Originally Posted by markbarendt View Post

when something breaks, or when I screw up, something random happens; the result isn't predictable.
The difference, as I see it, is between faults and characteristics. Any spot, limited area, center-weighted, or full averaging meter will behave characteristically of its type, regardless of what camera it is in. No AF system can know for sure which of multiple AF points is on the area of desired sharpest focus, so it must be told if that deviates from what would be most likely. That is a characteristic of all multi-point AF systems, though they may vary one to the next in what they choose, which the user must learn.

But when a lens does not focus where it is told, or when the meter blows exposure so badly in certain situations that the photographer can only learn about it the hard way, i.e., it is not characteristic of all systems of that type, that's a fault.