I haven’t totally figured this one out yet but I think the answer probably goes something like this.
Set out a timeline (length would depend on what you are trying to achieve, I like 12 months).
Set out what you expect to happen.
Then decide what is minimally acceptable.
If after 12 months you haven’t reached your minimally acceptable threshold it’s time to move on and do something else (new strategy, business, whatever).
Don’t fall for the sunk cost fallacy. Cut and move on.