A business plan or spreadsheet built without field evidence is "fantasy made explicit" — it converts an untested set of assumptions into a document that looks authoritative, and can lock an organization into executing something nobody actually wants. Because the arithmetic is internally consistent, it feels like rigor, but consistency between assumptions is not the same as evidence that the assumptions are true.
Osterwalder frames this bluntly: "Business plans and business cases are the death penalty of innovation." The fix is not writing a better plan but replacing planning-as-proof with real-world evidence gathering — see Evidence Spectrum for Validating Business Ideas — before committing resources, as part of the discipline in Explore/Exploit Dual Portfolio Management.