The way I described it to someone is that they feel "fragile" compared to Shimano. With my Ultegra brifters I felt like I could crank them with a crowbar and they would be fine, the Red shifters on the other hand feel fragile enough that I could break them if I wanted to. I have no doubt that they are strong enough to do their job and I've not heard of a single person having damaged them, just that they "feel" like I could damage them if I wasn't gentle.