The reason Lego works is a simple, well-defined interface. Two bricks stick together by friction because the stud pattern on one matches the hole pattern on the

The reason Lego works is a simple, well-defined interface. Two bricks stick together by friction because the stud pattern on one matches the hole pattern on the other precisely. Fortunately, that's a model that translates well to software. The way to make software reuse more like organ transplant than building Legos is to ignore the advice to keep the interfaces simple and precise. Or worse, don't even bother defining an interface, its data types, or error conditions.