Most of them are very good but the assumption that there is a mythical 100% good system or company would assume that requirements are reasonable, unchanging and

Most of them are very good but the assumption that there is a mythical 100% good system or company would assume that requirements are reasonable, unchanging and that the time and money to build it well are all present undermines everything. Even a simple application will quickly unwind when the whims of the customer change 10 times quicker than it takes to build something (same in most other industries).