Within economics modelling, attempts to model the feedback mechanisms that occur in the real economy are also really difficult — we know, for example, that investment in new
technologies will act as an incentive for the
existing technologies it hopes to substitute to become more
efficient (the sailing ship effect — i.e. in the 50 years after the introduction of the steam ship, sailing ships made more efficiency improvements
than they had in the previous 3 centuries) but how to quantify something even as simple as this is not easy BUT we have learnt a few ways to give sensible (order of magnitude) figures with time lags, the learning by doing effect and phased - in substitution effects based on massive amounts of data.