A friend of mine is a drag racer. His drag racing "hero" has a quote that he always repeats. "The best way to cut 100 lbs off a race car, is to find 1600 ways to cut 1 ounce."
There are thousands of ways Boeing cut a little here and there to achieve weight savings. Every aircraft designer before now, has made the same choices. If you don't think that way, you should design ships instead. Or maybe try being an architect. But not an aeronautical engineer.
It would be easiest thing in the world to add weight here or there to be conservative. But you cannot do that and succeed. To succeed, you have to find a way to do it lighter, and INCREASE reliability at the same time.
If the 787 did not have a few problems, I would lose respect for Boeings' engineers as not being professional enough.