The ancient wisdom is the practice of medicine is as much art as science. There is "evidence" supporting many practices. As in every complex endeavor, evidence is not static, but evolving constantly.
Evidence is necessary but by itself insufficient. We must use our own power of observation combined with what we know and what we've learned to decide what to do.
So your question is indeed profound, cuts to the core of the issues. Intuition is one way to phrase it. I once heard a colleague say we're not paid because of what we know, but for the judgement we exercise about advice or treatment to offer.
Each human is indeed unique. Even identical twins are in fact not exactly the same. Rules have limits when no two cases are precisely the same, it always comes down to that very intuition you are intuitively aware of.
After all, we frequently wish to have a second opinion. I do often enough too. I like the saying, get 5 experts in a room, and you're likely to get at least 6 opinions on any subject.
Who said decisions should be easy? I sweat over each and every one.