That's why it's useful to consider best case, worst case, best guess scenarios. It's also why different investors can come up with a wide range of valuations when they get down to considering an investment. In my personal experience, few financiers place significant reliance on projected financials - it's the underlying assumptions / notes that matter.

Just because it's difficult to forecast a year out also doesn't mean that it shouldn't or can't be done especially since investors themselves have to assume that they won't be able to exit within a year. Coming up with better projections for ROI just adds more datapoints from the very people/entrepreneurs who should know their space/market best (especially in more stable industries - I note that Wilson emphasizes that this is how he thinks of non-tech businesses).