Subtract the costs from your revenue and you get the profit, your actual gain. This is one of those laws we learn in school and that we all end up taking for granted. Then we actually end up forgetting about it, when we decide to start a business. And often we will start looking for a reason why our business is failing when it’s already too late. You wonder how the margins of your earnings could be so low, when sales were fine. You wonder why, despite fifty orders per day, your business kept dying, little by little every day, until the company accounts have inevitably gone in red. The reason is almost always there: hidden among the folds of those unaccounted costs that you somehow missed, that you did not consider.