If you are ever fortunate enough to hold one of the first 1925 Leica I(A)s in your hands, you'll quickly understand why it became the first commercially successful 35mm camera. (Just don't drop it. Each is worth $30,000 or more today!) It's oh-so-light, compact, and comfortable, and its few controls fall right where your fingers want them.
Its creator, Oskar Barnack, didn't throw the I(A) together as I suspect a lesser designer might have, nor did he follow the advice of a committee. Twenty years prior, while working at the famous Carl Zeiss optics plant in Jena, Germany, Barnack, an enthusiastic amateur photographer, spent much of his spare time hiking. Lugging around a plate camera and tripod proved slow and cumbersome.
Why not a pocket-sized camera that would use 35mm movie film? Barnack was confident that despite the format's small size, careful exposure and processing of the film might yield surprising results, particularly if he increased the picture area to 24x36mm, twice that of a movie frame.