First of all, this is a description of the man-woman relationship in terms of its requirements for exclusivity and completeness.
The relationship in the courting situation must be exclusive - i.e. it will not generally survive if one of the partners knows he/she is being double-timed. During courtship couples must be faithful. One can always tell who is going out with who at a party - it may not be possible to tell who is married to who.
The other aspect of the man-women relationship is that it can only exist at the level at which it has reached. As an extreme example, if a couple are living together, the relationship is unlikely to survive if the man decides to live in another part of town. At a lower level, a courting couple will have a certain degree in intimacy and frequency of meeting - both parties must continue to perform at this level for the relationship to survive. They cannot go back.
To some extent, as a courting couple, they must go forward. The degree of increase of intimacy and activities varies somewhat over the affair, but generally it is a steady increase. It may plateau for a while below living together, but generally the girl will want to push through such barriers.
If the man holds the plateau, eventually the girl will start looking for someone else, even if she's in love with him. Usually, however, she succeeds - unless the man is actively trying to get away from her (see Oscillating Syndrome) - and she may even then.
To survive, the relationship must be exclusive, it cannot go back, and it must go forward. It must be all or nothing.
In addition, at any point in time, the range of activities which are allowable is probably fairly arrow. This is illustrated in the above diagram.
Right at the start no sexual contact will generally be allowed. As the relationship progresses more is allowed - but then an area opens up which forbids a lack of sexual contact. As we have said, one cannot go back (only out of the relationship completely).
As time goes on the level of activity must increase. So the allowable range of activities forms a fairly narrow band.
It implies that both partners have the same view of the relationship - that their narrow bands broadly coincide with each other. If, because of some external reasons these are shifted and don't coincide, the relationship may fly apart.
A manager hires a girl, and they are attracted to each other. Now contrary to popular belief there are strong taboos in business management. Thus nothing happens between them. The girl leaves the business, and the manager takes the opportunity to meet her socially. Both however find the constraints of their former relationship difficult. But the girl, getting tired of the slow pace, initiates some sexual contact. He responds. But she now finds difficulty in following it through with her former boss. He interprets this apparent frigidity as that she wants to take things slowly.
She however has a different view. She hasn't yet had a proper date when she should have - and thus shows many of the symptoms of the Isobel Syndrome. He becomes especially embarrassed, and baffled by her behaviour, and makes no more advances. Under the influence of their former boss-subordinate relationship their narrow bands of allowable courting behaviour have been shifted apart - so the behaviour of one becomes in the not allowable region of the other.
In this example, the man would have been better off not jumping to the conclusion that she wasn't ready for a date. Some time considering her narrow bands of allowable behaviour and where it might lie should lead him to the possibility that it might have shifted with respect to his (girls don't normally initiate sexual contact with people they don't regard as their boyfriends). And when he gets the Isobel Syndrome reaction it should have been quite clear, and retrieved the situation by offering a proper date.
The work situation is a good example where a strong outside culture can impinge on the courting culture and shift peoples' perceptions. But there are others - such as peole from very different family or social backgrounds - which can cause the All or Nothing Syndrome to backfire.