The request almost always arrives as "we need a new logo". That is rarely the problem. What is missing is the system around it: the two typefaces and their uses, the palette and its proportions, the way a photograph is framed, the grid that holds documents together. Without it, every new item starts from scratch and the whole is never recognised.
A mark must then survive its real conditions of use. It will be seen at sixteen pixels in a tab, engraved on a stamp, embroidered on a garment, printed in a single colour on an invoice. A drawing that only holds large, in colour and on white is not an identity, it is an illustration. So we test every route in those four situations before presenting it.
Finally, tone of voice weighs as much as the visual and is almost always neglected. Two houses can share the same palette and differ entirely in how they write an error message, an invoice reminder or a reply to an unhappy customer. So we write those texts too, because they are the ones your customers read most often.