Are you sure it was the guy in the truck who broke it? Part of the reason writing "fragile" on a box does nothing to protect it is because the package also gets handled by machine on conveyor belts at the sorting facilities, and slides around on those belts alongside some pretty heavy packages. Machines can't read "fragile" signs, and so they don't know to treat your package with extra care. It's entirely possible a box full of engine parts, for example, slammed into your box at one of the sorting facilities.

There are ways to avoid that, of course, or at least get UPS to refund you for the damage, but it does cost more. Overnight packages get special treatment and are handled by actual people for most of their journey, so they don't get as banged up. If you go to a UPS Store and have them pack it for you, you'll generally always get up to the amount you insured it for back if it breaks because UPS Stores are supposed to pack things such that they can survive being on the conveyor belts.

If you want to pack it yourself, the general rule of thumb is that if it can survive the force of a four-foot drop, it will be ok. For fragile packages, you generally want to have four inches of packing material on each side of the item in order to absorb the shock. Not-so-fragile but still potentially breakable items can generally get away with two inches of packing material on each side.