everyone you come across is living their life in a fundamentally deficient way?
For starters, not with that attitude.
It isn't an attitude, it's Orthodox ecclesiology.
Dude, you better explain yourself...
Well Father, I'm not talking about being holier than anyone or anything as some people have assumed. It's my understanding that being in full communion with Christ and knowing the complete truth is an essential. How do you deal with knowing people you know are deprived of that?
Someone once told me the only sorrow we have on Pascha is knowing that there are others out there who don't experience the joy we do.
There are two further realizations we can come to when we realize that we are living amongst people who do not know the truth and are not in full communion with Christ. The first is to realize how short we ourselves are to being in full communion with Christ and knowing the truth. As Orthodox who have the sacraments and faith of the Church, of course we are not lacking as it depends on God's grace. But we certainly are lacking when it comes to following Christ's commandments. In "The Way of the Pilgrim" (it could be in "The Pilgrim Continues His Way"), the Pilgrim goes to an elder for confession and the elder gives him a list of three things to confess, which is a confession he has written for himself. The elder confesses that he does not love God, does not love his neighbor, and does not have faith. He gives reasons for his lack of all three, explaining how he falls short and misses the mark in each area. So, while we have the fullness of truth in the Orthodox faith and the grace of God in the sacraments, we fall very much short as depends on us. As Abbot Nikon says, we are all insolvent debtors before God.
The second realization that we can come to is that full communion wth and full knowledge of God are not really possible. We have what God gives us, which is as much as we are able to bear. As we are purified, illumined, and sanctified--beginning in this life and lasting throughout eternity--we still never attain to the absolute limit because God is infinite.
Now. God has given something to each person so that he might be helped spiritually in this life, so that he might develope a desire for God and come to know God and so be drawn to the Church and be saved. Even people who err morally or theologically (or both), who are not Orthodox, who may even be against Orthodoxy have something. It may well be that those who are not Orthodox, who just have one little thing which is just part of the whole truth, make better use of this little thing than an Orthodox Christian does of the fullness of the truth.
Beyond that, I guess how we "deal with" people who aren't Orthodox depends on specifics. I mean, they are still images of God, Christ died for them and wishes to save them, and He has commanded us to love them. We do not follow them in their errors, but we recognize the many good things they have to offer.