在开发大型软件的漫长过程中，面对极其错综复杂的问题，人的主观认识不可能完全符合客观现实，与工程密切相关的各类人员之间的通信和配合也不可能完美无缺。-large software development in the long process, in the face of an extremely complex issue, the subjective understanding can not be completely in line with the objective reality