A more thorough explanation:

Definition: A change from a customary or agreed-on course of action that is justified by circumstances.

Examples:

• Employment law: A departure from one's course of employment to tend to a personal matter. For example, if an employee needs to leave work early to take care of a sick child, this may be considered a reasonable deviation from their usual work schedule.
• Insurance: A departure by an insured party from a routine course of action, resulting in increased risk of some loss that the insured is indemnified against. For example, if a homeowner decides to leave their home unoccupied for an extended period of time, this may be considered an unreasonable deviation from their usual routine and could affect their insurance coverage.
• Maritime law: A departure from the terms expressed in a bill of lading or other transportation contract. For example, if a shipping company takes a longer route than agreed upon in the contract, but does so to avoid dangerous weather conditions, this may be considered a reasonable deviation.

These examples illustrate how a deviation from an agreed-on course of action may be considered reasonable or unreasonable depending on the circumstances. In each case, the deviation may have consequences for the parties involved, such as affecting insurance coverage or liability in legal disputes.