Planning is not guessing. Forecasting is guessing.
This may seem like a semantic argument, but I believe the distinction drives behavior.
Let’s say I am trying to figure out my staffing plan for user support for next year. I’ll look at my sales forecast (guess) and try to project (guess) how many tickets will be opened.
That’s only the first step though. Next, I’ll make a plan.
Let’s say I expect (guess) that we’ll need 5 more people next year. Right or wrong, I’ll make a plan that says, “We’ll hire 1 person in January and also initiate some design projects to help reduce tickets per user.
“In March, we’ll review the numbers and decide if we should add the second person we forecasted or whether the design improvements are bearing fruit. We’ll repeat that process in May, July, and September.”
The distinction is that the forecast is a guess, so it’s okay to stop when you get within a reasonable range of certainty so you can make your plan. Once you have that forecast, your plan should be detailed and rigorous. The fact that it will change as more information becomes available isn’t an excuse to skimp in the upfront effort.