In cybersecurity, a sunk cost refers to money, time, or resources that have already been invested in a security project or technology and cannot be recovered. These costs are 'sunk' because they remain regardless of future decisions. Organizations often face the sunk cost fallacy, where decision-makers continue investing in failing security initiatives simply because of previous expenditures, instead of objectively assessing current and future value. Recognizing sunk costs is crucial in cybersecurity budgeting and project management, as it helps teams avoid throwing good resources after bad and focus on effective risk mitigation. Properly accounting for sunk costs can lead to better decisions about whether to continue, modify, or abandon cybersecurity investments.