In my belief, Terminal Cash flow is the most difficult to estimate because it is highly sensitive to growth and WACC components. The other segments (initial investment and operational cash flows) are based on forecasted value and have a reasonable basic. On the other hand terminal value is input driven.

I am not certain on the sensitivity to growth - that may affect operating cash flow more! But yes, WACC will affect it more! How likely, or how much might WACC change though? Please explain.