I thought that all we had to do was develop non-combustion energy sources cheaper than fossil fuels, and everything else would fall into place. I think that's still mostly correct. But I underestimated how long people who are economically dependent on fossil fuel industries, and their political allies, could delay the transition. I think that those sorts of delay-and-obstruct tactics are going to ensure we far overshoot CO2 targets before (hopefully) beginning to correct them. That's even while the technologies of low-carbon energy continue to advance at a rapid clip.