In the distinctly professional duties, such as the ordering, classifying, and cataloging of books, there is a difference only in amount between the greater and the less.

And it is precisely these professional duties of which the person untrained in library work is in most cases wofully ignorant.
It is inevitable that in starting a library there should be some mistakes made; but with a trained librarian in charge, these mistakes will be fewer in number.

For example, what does the novice know of classification?
He realizes that the books, for convenience in use, must be grouped in classes.

If he has had the use of a good library (as a college student would) he has some idea as to how the class divisions are made, and knows also that there must be some sort of notation for the classes.

Necessity being the mother of invention, he contrives some plan for bringing together books on the same subject.
But with the addition of books to the library and the demand which growth makes, he finds that constant changes have to be made in order to get books into their right places; and then some day he awakens to the fact that there is some perfectly well-known and adopted system of classification which will answer all his purposes, and be a great deal more satisfactory in its adaptability to the needs of his library than the one he has been struggling to evolve.