The best way to put this is that there are NO two schools of thought on any issues that one is required to believe. (such as the Trinity, the Nicene Creed, etc.) The Church has ruled on this in Ecumenical Councils under the guidance of the Holy Spirit.
There are simply oooooooooodles of things that the Church has NOT decided in Council.
Now, one's spiritual father has read various opinions (remember, the Church is infallible under the guaidance of the Holy Spirit, but no single member of the Church is anything other than a fallible human being). One's spiritual father has also got a very good (one hopes) knowledge of where you are at, spiritually, and what your sources of temptation are.
Now...I'll give an analogy. Your spiritual father is like your doctor. You choose him for his ability to heal your soul with the best possible medicine, and keep you healthy. Now, anyone who has read medical literature knows that there are MANY medicines to treat any given illness. The doctor must make the best decision possible, using the information you have given him, to maintain and increase your physical health.
Your spiritual father does the same. If the issue is not dogma, then he decides what will best aid you on the path to theosis, through his knowledge of you.
The difference between the protestant point of view is that in Orthodoxy, we NEVER think WE have our own answers as to what is best for us. Sort of like we will never, ever, decide we can diagnose and treat our own life-threatening illnesses without a doctor.
Again, in Orthodoxy, we have the issue of obedience. When one has a spiritual father, one places himself entirely in that person's care. We tell the whole truth, and then we GIVE OBEDIENCE. Orthodoxy teaches us that if we are following the direction of our spiritual father with as much good will as we can, then we are not held spiritually accountable for our issues stemming from that obedience.
For instance, this story about St. John Maximovitch illustrates some of that advice turned personal:
Archpriest George Larin, who had been an altar boy of Vladyka’s in Shanghai, relates: “Despite Vladyka’s strictness, all of the altar boys loved him very much. To me, Vladyka was an ideal, one which I wanted to emulate in every way. Thus, during Great Lent, I would not sleep in bed, and instead lay on the floor. I would not eat my usual meals with the family, but instead would partake of bread and water in solitude….My parents became worried and took me to Vladyka. Hearing them out, the prelate asked the guard to go to the store and bring a sausage. In response to my tearful cries that I did not wish to violate Lent, the wise prelate admonished me to eat the sausage and to always remember that obedience to parents is more important than personal accomplishment. “How then should I proceed, Vladyka?” I asked, hoping nonetheless to “especially” apply myself. “Go to church as you always did, and at home, do what your mother and father ask.” I remember how grieved I was that Vladyka did not assign to me some “special” deeds to accomplish.”
In this case, we see pride in ones fasting actually being a spiritual sin. Does the Church specifically outline the fast? YES! (as it gives the exceptions, as well). Does the Church also recognize that pride in being so strict is a sin? You bet. But that is an individual call, not for an individual to make, but for one who knows that individuals soul, prays for it, and does his best to guide it aright, as mistakes rebound on his own soul...one's spiritual father.
Thus, we note that as in medicine, no matter what sort of wonder drug many doctors swear by, if it will harm the patient, the patient's doctor will not give it to him.
In Orthodoxy, we rely on our spiritual father to "prescribe" for us. And God rewards the trust by not saying "You listened to your spiritual father and ate meat during the fast...that's a sin!". The opposite is true. We are told obedience is better than sacrifice, and we do not even need to confess that we ate the meat, under the direction of our spiritual father.
In protestantism, Sola Scriptura makes the individual the final authority on what God is, or is not "convicting" him to do.
Orthodoxy says otherwise...our priest, who has the grace of Apostolic Succession upon him (which we do not) will tell us what we should do for the health of our souls. We follow, in obedience.
Does that help?