I can only speak of my own failings, but I have a tendency to assume that what is known or obvious to me, is also known or obvious to others. This has had unfortunate consequences in the past. For instance, I once assumed that someone knew the difference between 'margin' and 'markup', so rather than patronise them by passing on the vital information, I let them get on with producing a price list that was of no use what so ever, as all the prices were too low. Rather than punish the other party for my mistake, I revised the list myself, then showed them what the difference was.* With the hindsight of many years, I should have got them to revise the list, so that they had multiple chances to apply what I'd just told them. Having to plow through 300+ items making the same calculation tends to lock these things into your mind. * 'Margin' is the percentage of the total selling price that is profit. 'Markup' is the percentage you add to the cost price in order to establish the selling price. Let's say we both work for Guitar Center and I tell you to create a price list for our shops by applying a 'margin' of 25% to the Fender Trade Price List. But you don't understand and apply a 'markup' of @25%. Let's see what a disaster that would be. A $750 guitar with a markup of 25% = $937.50. A $750 guitar with a margin of 25% is $1,000, which is about 33% markup. Ooops! What's obvious to me may not have been at all obvious to you.