But cooking? You very well may need varying ratios of ingredients, to taste, depending on size/freshness/variety of the produce you are using in a recipe. Or simply your mood.
Whatever tomatoes grandma was putting into a marinara 50-100 years ago are nothing like the varieties you are going to find at the grocery, farmers market or your garden today anyway.
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https://www.buzzfeed.com/jesseszewczyk/buzzfeed-foods-best-c...
Tasting/feeling as you go and adjusting is probably one of the most important bits of cooking or baking.
For example, hydration of the dough will dictate the final outcome of the bake. Every flour hydrates differently depending on protein, ash content, milling, and so on. So even if a recipe calls for generally 70% hydration, it may be more or less depending on the “feel” of the dough if you switch flours. Croissant dough detrempes need to be hydrated at a very low percent, generally under 60%. The flakiest croissants tend to be made with a very dry stiff dough hydrated at 50%.
And beyond the choice of flour—temperature (proofing, desired dough temperature), climate, kneading/mixing, yeast or wild starters, salt will drastically change the substance of the bread.
We haven’t even talked about gluten formation (especially with regard to autolyse and dough folding) and fermentation techniques… and how the raw dough is loaded into an oven and at what temperatures (deck, convection or fan-assisted, with humidity, Dutch oven, etc).
Every loaf of bread I bake probably tastes slightly different, and that's just fine according to the people eating it. If I'm baking a cake, or cookies and at the last minute, I discover that I'm out of something important, I just figure out a substitute and it turns out (usually!) just fine.
Far more important than precision is understanding how various ingredients will react with each other and compensating.
If you fail, you note and adjust.
After a while, you know that it's situational - unless it's salt or leavening agents(yeast, baking powder, etc.), there is a bit of wiggle room to adjust things.
The idea of combing through dozens of recipes, formulating a precise grocery list, and shopping with the intent to cook that one exact dish is very much a Type-A modern day phenomenon.
How many tomatoes go into the sauce? However many bruised ugly tomatoes grandma had leftover. How much meat to make it a meat sauce? Whatever leftover cuts from the roast. Etc.
Improvisational cooking was much more the norm. It is also how you avoid food waste.