Willingness to fork, which requires human choices/intervention. Seems to me the extinction of forking is (was) a design goal of BTC. I know of no example of that with alts. In fact, there seems to be zero appetite for this goal with alts.
Vitalik has talked about the balance between innovation and stability and has said that it is a goal for ethereum to become more stable over time. The danger is just doing that too early and ossifying around an inadequate design.