Substituting a complex measure with a simpler proxy that becomes the goal itself.
Distorts organisational behaviour, creates perverse incentives, and explains why metrics often become meaningless once they're targets.
This bias explains Goodhart's Law: 'When a measure becomes a target, it ceases to be a good measure.'
"Your confidence in your own rationality is inversely proportional to your actual rationality. Ironic, isn't it?"