Understanding why terrorist operations succeed or fail

Understanding why terrorist attacks succeed and fail is important for homeland security and counterterrorism planning. In examining past terrorist attacks, this understanding is necessary to discern why attackers sometimes are very successful and why sometimes even reasonably well-planned operations fall apart. Discerning ways to make attacks less likely to succeed is a central goal of efforts ranging from homeland security technology development to the direct military engagement of terrorist groups. This paper argues that the past success or failure of a terrorist operation-- or the likelihood that a future attack will succeed-- can be best understood by thinking about the match or mismatch between three key sets of characteristics: terrorist group capabilities and resources, the requirements of the operation it attempted or is planning to attempt, and the relevance and reliability of security countermeasures.