Flexibility is a key asset in dealing with uncertainties in investment, operations, and decision making. Traditional Transmission and Distribution (T&D) planning today faces unprecedented uncertainties driven by decarbonization and political/economic volatility. Years of low or negative load growth are forecast to become historically high load growth driven by electrification of transportation and building sectors and, in time, agriculture and industry. Generation planning and how it drives T&D planning are subject to uncertainties around renewables adoption, especially when individual consumer decisions determine investments in distributed photovoltaic (PV) and storage. Technology development introduces uncertainties around performance and cost improvements in all these areas. Volatility in public policy can drive volatility in, for instance, electric vehicle (EV) and PV adoption as incentives and mandates change with changes in federal, state, and local politics.