The symbols of fate in In another country include;
The medals- Symbols of bravery BUT also symbols of inequality and injustice. The American soldier, as opposed to the Italian soldiers, received his only for being American.
The wounds-Are symbols of bravery and of distancing from soldier to soldier. The American soldier received a smaller wound than the Euro soldiers, and yet he knew inside his heart he was still more scared of death and war than the soldiers who've lost their noses, parts of their body, etc.
The grammar was the Major's symbol of self and outer control. He has lost control of the world as he knew it, and grammar is perhaps an unconscious way for him to keep some form of normalcy and control in his life.
" A man must not marry" was his way of telling the Narrator that one cannot put himself in a situation where one can lose something. He was referring to his wife to whom he married after he thought the war was out of his life, and yet, she died unexpectedly.
In my opinion one simply cannot live like the Major. It would be a never ending chase to try to control what depends on so many other variables. Life is only at the center of a nest that holds many other social, psychological, physical, and behavioral building blocks. One cannot control all of that. He is limiting himself even further by trying to control everything.