A recipe:
- Preheat oven
- Mix stuff
- Mix more stuff
- Put everything in the fridge for an hour
- Do a bit more prep
- Finally, bake for 15 minutes.
Why did you ask me to preheat the oven more than an hour in advance? And why didn't you catch this oversight when you tested the recipe? Oh, because you didn't bother to test it, of course.