Use 'arbitrariness' to show that a decision is unexpectedly made without a clear reason. His arbitrariness in selecting team members baffled us all.
Pro Tip 2/3
Negative Connotation
'Arbitrariness' often implies a negative judgment about a person's decision-making process. The arbitrariness of the manager's policy changes upset the employees.
Pro Tip 3/3
Subjectivity
Emphasize the personal, subjective nature of a choice with 'arbitrariness'. In art, the arbitrariness of color choice can be a statement of style.