In the math world, you have things like identity functions and zero functions. Identity functions basically do nothing to your number–you put something in, you get the same thing out. Zero functions discard what you put in and give you a known constant output.
In the juice world, you have much the same. You have identity food items and you have zero food items. The identity food items do very little to affect your beverage. Water is a perfect example of this. You can add water to give you more volume, but unless you go way overboard, it will not change the taste.
Then you have radishes. Radishes are the zero function. Anything plus radish equals radish. You just cannot escape the inevitable result of radish, no matter what you add.
I have yet to find a mathematical parallel for celery — maybe some kind of reverb or echo. Any juice with celery in it gives you an aftertaste of celery, which makes you feel like there is a string of celery in your teeth for the rest of the day.