Your friend shares a recipe: "This chocolate cake always works."
You follow it exactly: Same ingredients, temperature (350°F), time (30 minutes).
Your cake: Dry and overcooked. Your friend's cake: Perfect.
What you didn't know: Your friend lives at sea level with an old oven that runs 25°F cool. You live at 5,000 feet with an accurate oven.
You copied the recipe. You didn't account for the kitchen.