Many of the good things in software development come from people who notice how programmers work and extract certain lessons from it; in other words, looking at the practical approaches and extracting common and useful lessons rather than speculating a solution.
The so-called Gang of Four (Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides) took this exact approach when they documented, in a precise language, a list of design patterns. After noticing how more programmers were solving the same problems in similar ways, they decided to write these patterns down and introduced the world of programming to the idea of reusable solutions to specific problems within a clear context.
Since the design paradigm of the day was OOP, the Design Patterns book they published shows these solutions using object-oriented approaches. As an aside, it's quite interesting...
