How good is good enough?

What is excellence? How do you know if you've worked hard enough and
tried hard enough? While working onboard the Doulos, I often heard
people remark in this manner. They would comment on how the task was
above them, they couldn't do it and yet, by God's grace the job was
done. I don't want to criticize this view, as I've been there many
times. But there is something in that attitude that perturbs me. It
seems to say that we should be placed in jobs that our beyond our
ability so that God is the one who does the job.
This is all very nice, but couldn't we also say that we do our best
and no matter what we do, God is the one who gave us the ability to
do and will what we did? I don't know if this makes any sense. What I
suppose I dislike is the attitude, "I'm not qualified for this, I
have no idea what I'm doing." I would contrast that with, "I can do
this. I've studied, worked myself to a place where I can confidently
say, 'I can do this, through God who strengthens me.'"

Continue to work out your salvation with fear and trembling, for it is God who works in you to will and to act according to his good purpose. (Phil. 2v12)

This is perhaps obvious for some and dumb to others. Again, I've
spent three years with the Doulos, where we're repeatedly placed in
areas out of our expertise. But in a general way, I think we should
take some confidence in our abilities and simply work our self hard.
And when we succeed in the end, we give God all the credit.
What I mean by this is simply:
Should we have a God who uses us in our weaknesses or a God that gives us strength? Are these different or the same thing?