That's a really short sighted way of looking at it. it is not about random probabilities but instead WE lack the ability to measure and account for all variables that contribute to plant health. Can you tell exactly haw much light is reaching every leaf? Can you calculate the exact amount of CO2 and nutrients traversing the leaf/water interface? Can you determine exactly the amount of nutrition being taken up by the roots? The answer to all of these questions is a resounding no, not unless you have £50,000 worth of measuring equipment. As a result, EI starts with a worst case analysis and doses at levels that will satisfy all but the most stringent conditions. If the environmental conditions of your tank are not near the extreme limits then it's possible to back off the dosing levels. But because you are unable to determine exactly where your particular tank lies with respect to the extreme limits you must then experiment with the dosing levels to see how far below the limits you can go. EI is about understanding the relationship between dosing and health, and so the plants will let you know, through their response whether your decisions are wise or foolish.
Have you, or anyone you know ever been on a diet? How can you tell whether you are eating exactly the right amount of food or not to maintain health while losing the right amount of weight at the right speed? It depends on your activity and your level of fitness and your starting weight, so no one amount fits everyone. This is exactly the same thing (except in reverse). We are feeding plants so that they grow faster and stay healthy.
Stop thinking of EI in terms of magic numbers and rigid formulas. It is a concept of nutrition and health so it requires your intervention, observation and analysis. We are farmers. Simple as that. Like farmers, we try to optimize our yield and sometimes it requires corrective action depending on the amount of sun or rainfall. The farmer growing tomatoes in Lincolnshire probably does things a little differently than the tomato farmer in Greece, not only because they each have different conditions, but because they may have different goals as well.
The thinking EI hobbyist tries to understand WHY something works, not just "if it works then use it" because what woks in one tank may not work in another. 8)
Cheers,