What's even harder is that you're usually trying to forecast for a reason other than pure academic curiosity. Like, should I be worried about the coronavirus? Should we stay inside? When can we reopen business? But the decisions people take determine the curve and the predicted curve determines people's decisions. If you decide not to social distance, you're changing the future. For that reason, forecasting is better done under different scenarios. For example, don't tell people approximately X (+/- a lot) will die. Tell them approximately X (+/- a little less) will die if we don't social distance and approximately Y (+/- a little less) will die if 95% of us self-quarantine.

It's harder than just fitting a curve, but that's kind of the point. If you want actionable predictions, it is harder.