GetWorkOnItemResult.cs

private OneOf<WorkCompletedResult, ProgressMadeResult, SetbackResult> 
        GetWorkOnItemResult(CrewContext context, WorkItem item)
{
    var roll = context.GetRandomNumber(1, 20);

    // Something went wrong. Likely a mistaken assumption or bad requirement
    if (roll == 1)
    {
        return new SetbackResult(Priority.High);
    }

    // We got a massive success or we've previously made significant progress
    if (roll >= 20 - item.ProgressMade)
    {
        return new WorkCompletedResult(item);
    }

    // Okay, not a great roll, let's call it a setback
    if (roll < 3)
    {
        return new SetbackResult(Priority.Normal);
    }

    // Just a bit of progress
    return new ProgressMadeResult(item);
}