This is something i have tried explaining multiple times, but I cant really say that i understand the point. It's harder, so it takes longer, right? My response is that it is a combination of time to complete and probability that the estimate is wrong and it takes a lot longer. But it seems to me that it would be better to decompose those aspects. The benefit of putting it in one number is that it is easier ti use to manage expectations. It's like giving an estimate that is higher than your true estimate based on risk. Frequently, you should end up with spare time that you use to offset the reputational impact of totally missing sometimes. From a manager's perspective, it looks a bit like padding the estimates systematically, to offset all the biases in the system towards only hearing the earliest time possible.

Max L