I've got a different angle on this question. I figured out about a month ago that I'd gotten too light because I came to like gear as much as I like getting out and hiking!
I learned nearly everything I know about backpacking through this community. Hooray! Unfortunately, I also became very gear-centered over the course of 2 years of reading, researching, buying, testing, and reselling. About a month ago, when I finally organized my entire gear inventory and put it on a big steel shelf unit, I was disappointed to see so many items (mostly small stuff, thankfully) that I'm not sure I'd ever get the chance to test out, because I accumulate gear faster than I can go out and test it! I think this might be a pretty common problem in this community . . . but I could be wrong.
I also realized that planning a BP trip had become a huge chore for me simply because of selecting from my possible choices what I was actually going to take! It had become downright annoying!
And on top of that, I feel like my gear-centered-ness had taken me very far from what I view is the heart of backpacking, which I guess is something like: getting out there and doing it, and not wasting time and effort fiddling and controlling the mess out of the endeavor. It's ok if it's messy--that's part of the fun.
Keeping all this in mind, I'm now selling about 80% of my gear on the Swap forum right now, and replacing most of my choices with single items that are simple, lightweight, satisfying, and long-term usable, unlike some of the tiny, thin, light, tinkery SUL pieces that I had before.
Now I know I'm not everyone, but this has been my experience in realizing that I've gone too light. I've now accepted a couple pounds of "fat" back into my gear for the sake of the piece of mind, simplicity, utility and durability that these items offer.