Probably, for many or most people in The West, in a secular society in which there is little support and much discouragement for Christians - some Christians will find themselves more-or-less outside of all possible churches which are real Christian churches and worth being members of: whether or not they attend a particular church, or support a particular church; at the bottom line they will find themselves to be de facto non-churched Christains.
I think this arises when a Christian does not (in his heart) believe any of the specific denominational teachings with respect to the necessities for salvation - when he does not believe in the necessity of membership of a specific church denomination in order to be a Christian and to be saved.
In other words, this non-churched Christian does not believe he has to be baptised (e.g. baptism administered by a particular kind of person, in a particular way, in the context of a particular institution - or perhaps like the Salvation Army Christians, he does not believe baptism to be necessary at all), or partake of the sacraments (ditto), or indeed any other particular thing done in an institutional context - he does not believe he must have a particular theology...
This, then, is a negative set of beliefs which conclude that nothing specific that is available only from a specific church institution is necessary for salvation: the necessities cannot be provided insitutionally and nothing institutional is strictly necessary.
But instead that whatever is necessary for salvation is some-thing/s between himself and God - that he is, in fact, already saved, and has 'only' to accept this gift from Christ, all of which he has done by becoming a Christian (outwith any particular church).
It seems - from their actual behaviour, from their actual practice - that many Christians in The West are of this type: and I do not mean 'liberal' Christians, but traditional and orthodox and catholic and evangelical and fundamentalist Christians of all types... at a pinch, when things get difficult, the behaviour seems to indicate that a specific church is not absolutely necessary - not worth dying for.
This is an interesting state of affairs, because it means that - by a strict and wholly honest interpretation - such a Christian is excluded from all denominations which are worth converting-to.
If he is already in a denomination (as a cradle Christian), then he is probably okay, since the requirements to stay in a denomination are much less strict than the rules for converts (which situation in some senses is illogical and wrong, but in other senses is understandable and probably necessary).
This is very troubling to me, since I believe that everybody should become a Christian, but not everybody who becomes a Christian will be able to join a church (certainly not in the fullest sense of membership - but perhaps not at all: perhaps there will be no denomination at all which this Christian could honestly say he believed and which he could honestly satisfy as to his eligibility).
(To rephrase Groucho, a non-churched Christian might say: "I would not want to join any church that would have me as a member; and any church which I judge to be worth joining would certainly not allow me to join it - assuming I were completely honest about my beliefs and commitments.")
In practice, then, and in the many particular circumstances of many specific people - they may become Christians, real Christians - be born again - but then they will get stuck, will not be able fully to join any worthwhile church, will be (at the bottom line) on their own...