I can validate most of a design now and sign off with real confidence. But the strange failures, the ones I can't make happen twice, still slip through and show up later in the field. I chase a bug that vanishes when I look for it, and then it comes back the moment it's out in the world.
More people experience this than they realize.
You can validate most designs but the failures you can't reproduce still get past you.
If this sounds familiar, the Library can help you find the bigger picture.