When a defect is found during the user requirements analysis, all it takes to fix it is to update the requirements document. However, if that same defect is missed until the whole product is developed, fixing it may require a change in the design, a rewrite of significant amount of code, customer re-approvals, and re-testing of the product once the fixes are complete. The more complex and more expensive is the product, the greater is the cost of finding defects late.
Stecklein, J. et al. (2004) conducted a study for NASA type of products (e.g. spacecraft or satellite) and found that if finding an error in requirements phase costs 1 unit then it increases so significantly that the same defect if undetected until operations phase can cost to fix anywhere from 29 units to more than 1,500 units. So if a unit costs $1000 then at requirements phase a defect would cost a $1,000 to fix while in the operations it can cost from $29,000 to $150,000 to fix.