A recipe is a compressed description of a process, and a large amount is left unsaid. The omissions are deliberate, and they explain most first-attempt failures.
Preparation state is assumed
An instruction to add chopped onion assumes a particular size of chop, which affects how fast it cooks, how much it browns and whether it disappears into the sauce.
Similarly, ingredients are assumed to be at a particular temperature, and food taken straight from the fridge behaves differently from food that has stood.
These assumptions are invisible because the writer performs them without thinking, and they are among the largest sources of variation between two cooks.
The intermediate targets are unstated
Experienced cooks aim at checkpoints throughout a dish, knowing what the pan should look like at each stage before proceeding.
Recipes compress those checkpoints into a single instruction, so a cook who is slightly off at step two has no way to detect it before step six.
Which is why detailed descriptions of appearance and smell are more useful in a recipe than additional precision in the quantities.
Corrections are absent because they are constant
A cook adjusts continually, adding a splash of water when a pan runs dry, lowering the heat when something colours too fast, and correcting seasoning several times.
None of this appears in the written version, since it responds to conditions rather than following a plan.
A reader following the text exactly therefore executes a process with its feedback loop removed, which is a genuinely harder task.
Equipment assumptions are embedded
Recipes assume a pan of a certain material and size, a hob of a certain power, and an oven that behaves in a particular way.
Change any of those and the stated times and heat levels drift, sometimes far enough to change the dish rather than merely delay it.
This is why a recipe that works reliably for one cook can behave differently in another kitchen without either having made a mistake.
Reading a recipe twice closes much of the gap
Reading the whole recipe before starting reveals where the pace changes, which steps require attention, and what should have been prepared in advance.
It also exposes the omissions, since a step that jumps abruptly from one state to another is usually where the unwritten work sits.
Writing the checkpoints into the margin after a first attempt turns a generic recipe into one calibrated to a particular kitchen, which is what repetition actually produces.