Reliance on false or old assumptions about the world can be as misinformative as dependence on false or old data. It can lead to drastic errors in forecasting.
The announcement by Iraq, in 1991, that it had secretly used an antiquated, old-tech method of uranium enrichment to produce weapons-grade uranium, overturned in one stroke the decades of assumptions about which procedures and materials need to be safeguarded. The electromagnetic enrichment method used by the Iraqis is openly described in scientific literature but it had been assumed that this information did not need to be covered by the secrecy and controls related to nuclear safeguards.
Critics of the UK's welfare system claim it is based on assumptions about human behaviour. They say the system was developed by those who assumed that people would behave altruistically; subsequent changes to the system were developed by those who assumed people would behave selfishly. Neither assumption being entirely and always accurate, the system is doomed to fail.