When you buy a car, what is the main feature you want? For me and many other people, the first thing you want is for it not to break very often.
I hypothesize that this generalizes to many other areas.
As a user, what do i want from a computer system? The first thing i want is not to spend hours trying to fix it when it gets messed up.
As a software developer, what do i want from a library? The first thing i want is for it not to crash my program.
As a grad student, what do i want from a software numerics library? The first thing i want (after not crashing, which is the desiderata for a general library) is for it to give correct answers for the queries it purports to handle, and to give an error if it can't handle it.
When i pick up a pen or pencil, what do i want? The main thing i want is for the pen not to be dry and unusable, and i dont want the pencil tip to break off very easily.
When i buy food, what do i want? The first thing i want is for it not to make me sick.
When i use a toilet, what do i want? The first thing i want is for it not to overflow when i flush it.
When i take a prescription drug or go to the hospital, what do i want? The first thing i want is not to walk out with a worse problem than i walked in with.
When i make an investment, what do i want? The first thing i want is not to lose the money i put in (note: in the field of finance this may be what you want but it is hard to get, for fundamental reasons).
When i buy a disk drive, what do i want? The first thing i want is for it not to crash.
There are cases where this isn't true. Changing a lightbulb is no big deal, so I'd rather have one that is the right color, bright, cheap, and energy efficient than one which is dim and a weird color and an energy hog but that never burns out.