if it doesnt break, dont touch it

there are 2 choices:
1-if it doesnt break, dont touch it.
2- better try to make it so does not break!
which 1 you choose?
the truth is, both have valued points.
and we do 1 or the other all the time
lets consider 1 situation:
you have been flying certain plane without making any change or 'improvement' and it has been doing just fine...
or another: something has happened to you and you want to take measures to prevent it to happen again (or some say that this or that failed to them so you better do something to prevent it to happen to you).
so, what will you do?
i have some planes that have been flying without fault and keep them as they are.
on the other hand, i have had some failures with a plane and try to prevent that to happen again by doing whatever i can.
isnt this confusing? why 1 with 1, and another with another?
what do you do?
are we a puzzle or what?
or is this a matter of probabilities and risk factor?