"A foolish engineer and his log book are soon parted," is the motto that the design engineer I share a workspace with lives by, and being a design engineer myself I tend to agree.
Engineers, scientists, researchers, inventors, or anyone else that designs or creates will undoubtedly keep a log book of their work, a hard copy record detailing their ideas, theories, hypothesis, random wild guesses, calculations, experiments and observations. In short it is a record of their work, the lifeblood of their professional career.
Why is there such a need to record the details of their work? Well, there are a few reasons why. For starters, our memory and recall process is seldom photographic. When we work on something we do not have the ability to instantly recall all the details of our work, a log book then is a wonderful resource to aid us in the recall process. By following the carefully recorded entries in our log book we are able to reproduce the sequential steps in our thinking. This process becomes extremely valuable when we are trying to reproduce an experiment, or are trying not to duplicate a failure. Along the same lines, it helps us to continue a particular train of thought we started on.
Secondly, there is always the need to share the information with others. Seldom is there one person solely responsible for a design of any particular large magnitude. I am not saying that there is not the occasional inventor that works in secrecy out of his basement, there is, they are just the exception rather than the rule. Since we need to convey ideas, whether to a colleague, or in a report to a superior, it is always wise to have a recording of our work. In fact many companies that I know of would insist on a formal system for recording such information. Imagine if you will a corporation that has spent millions working on a design only to have its lead engineer or researcher leave or die. Where would the corporation be if accurate records were not kept?
Finally there is the need for inventors to fill for patents on their inventions. A patent is a licensing right that will exclude others from using, making or selling the idea. In a typical patent application, a patent specification needs to be included. This specification is a written description of the invention in such details as to allow for a person skilled in that particular discipline to make and use the invention. A good log book then not only provides the details needed for the written specification, it also comes in handy as a record of the invention should legal squabbles between individuals or companies arise over the filing of a patent.
Log books then are the backbone of most ideas that are brought to fruition. Without log books many wonderful ideas might be lost forever.