It has been said that Thomas Edison made 1,000 prototypes before he had success with the light bulb. It is also true that Charles and Ray Eames experimented with all sorts of applications for plywood long before the first DCW chair was made. In today's world, trial and error is not often something that is celebrated. We try to teach our kids to come up with the right answer as opposed to testing out all the wrong ones first.
When I was in junior high, I had a math teacher who told me that the answer is not as important as understanding how to get it. Years later, I had a professor at college tell me that an expert is someone who has made every possible mistake in a very small area of study. To this day, I don't think I could argue against either statement. I have read dozens of books on leadership, business, and success and each of them say the same thing in one way or another.
With this in mind, how can designers be expected to deliver a perfect masterpiece every time without incident for each client? The answer is that we can't. Every project is different and has different challenges. Many firms take a 'cut and paste' approach to their work in order to avoid mistakes. While this approach is common, it does not promote an environment of creativity.
In order to be creative, you have to make mistakes. If you have ever watched your kids, you will see that they have a certain way of learning that adults have long forgotten. It starts with the phrase 'what happens if I do this?'. Adults don't often ask those questions. We are trained to learn how to anticipate what will happen without having to do the test. Educational expert Ken Robinson has said 'If you're not prepared to be wrong, you will never come up with anything original'. As a designer this is as important a statement as 'Form Follows Function'.
Louis Kahn was notorious for making big changes on projects well into the construction phase of his projects. If the process revealed something that he had not seen on paper, he would alter it in the field. Although his clients did not welcome this exploration (and the resulting change orders I'm sure) there wasn't one who didn't rave about the end product. Great design evolves. It is not a static process.
In summary, if you want to be a great Designer, you have to get your hands dirty. You have to do the work. You have to adjust and not be afraid of being wrong. These are all traits that are counter cultural and will force you to unlearn what you have been taught. It's not that great Designers don't follow the rules - it's that they understand them so well that they know how to break them. Just be prepared for the fact that it might take 1,000 attempts to do something ground breaking.