This. Or the guys that run the radar even though you're on top and can see it's only stratus as far as the eye can see.
Try walking around the back of your jet sometime in light turbulence caused by "only cirrus". Or better yet, put down the McPaper, crack open a book or your perf charts and re-educate yourself on coffin corner, high-and-low speed buffets, etc. If you're anywhere near your ceiling for either the jet or your weight 1.1 G is all it might take to send you lower ala Pinnacle.... dude.