What makes a threat vector realistic is the idea itself and the probability of success.

FORBES: Connect

We again also developed a very simple system for classifying threats generally based on domain of operation (noting that some arguably operate in multiple domains) in an effort to see if any broad spectrum solutions could be developed to neutralize more than one threat vector.

FORBES: Written by David Lowenstein and Risu Na

For example, even though a Nuke would cause ninety billion dollars in destruction the probability of this type of attack is so low that it creates a vector value below the benchmark needed to consider it a daily threat.

FORBES: Connect