An assumption is a condition a system relies on without checking it in every case. In software, hardware, and robotics, assumptions can be about user input, sensor readings, network state, time, or the environment. They help systems stay efficient, but they also create risk when reality changes. If an assumption is wrong, the system may behave incorrectly even though its code still “works” as designed.
In cyber security, assumptions matter because attackers often target them. They may send unexpected input, alter the environment, or exploit a missing validation step to make a trusted condition false. Defenders reduce this risk by verifying inputs, defining strict trust boundaries, and designing for failure instead of perfect conditions. A secure system does not assume too much; it checks what it can and limits damage when it cannot.