Why Your Toughest Bugs May Live in Assumptions, Not Code

A developer writing on DEV Community argues that many persistent software bugs stem not from faulty code but from unverified assumptions about how systems behave. Common culprits include incorrect expectations about API response structures, null values, environment variables, and third-party library behavior. The author recommends a disciplined approach: write down the assumption, inspect the actual data, and only modify code after confirming the mismatch. Using a simple API example, they illustrate how assuming a response shape without verifying it can cause confusing undefined errors. The core takeaway is that effective debugging often means auditing your mental model of a system, not just scanning for syntax errors.