The mystery was paradoxically deepened and yet clarified by the observation, made by a very brilliant scientist whom you have never heard of, so don't bother to look it up, that the relationship between the size of the purse and the amount of material it can contain is inverse, rather than direct as one would expect. Often a large handbag can only contain enough supplies for an overnight stay at most, yet it is frequently demonstrated that a small purse can contain several times it's own volume in terms of wallet, checkbook, tampons, make-up, and so on. This explains the usefulness of the purse, but the mystery remains as to just how the the purse contains more space on the inside than on the outside. One theory is that the purse possesses some unknown topological trait which allows this. Precedent: the moebius strip, which has only one side and one edge, but can be made easily using a simple two-sided strip of paper. Perhaps even more relevant is the klein bottle, a hypothetical construct related to the moebius strip, which has only one surface and no clear inside or outside. This is decidedly similar to the purse, in that a klein bottle's lack of a clearly defined inside means that it arguably contains the entire universe, itself included. Unfortunately, topologists have proven that true klein bottles cannot exist in three dimensional space, although approximations have been constructed.
This study has exciting ramifications. For example, if the relationship between a purse's external size and internal size is based on a geometric rather than an arithmetic progresion, then it is conceivable that a purse the size of a thimble or smaller could contain the entire universe. This would prove that is not only a woman, but a woman who lives in California, Paris, or Milan, since no one else would carry a purse smaller than a thimble.
As exciting as this is to theological seekers, there is an even greater conclusion that can be drawn from this discovery. We have no reason to assume than this phenomenon applies only to purses. In fact it has been observed regularly with men's knapsacks, wallets, the belly bags that were a fad for a brief period a few years ago, and Mary Poppin's carpet bag. And since the relationship between inner and outer pursial space is inverse, there must logically come a point at which the amount that the purselike container can carry is less than one would expect when the container is sufficiently large. Which explains why you can never fit all of your things into a large suitcase when you are going on vacation.