Dtail
Give me a museum and I'll fill it. (Picasso) Give me a forum ...
FIREcalc is based strictly on US market history and a very long period of it containing all sorts of difficult financial conditions along with the good times, so I’m not sure why you consider it optimistic.
Note - there are no investment return assumptions.
+1
Perhaps it is seen as optimistic vs. a few other calculators which use Monte Carlo simulations, which by default are more conservative.