It was more than 20 years ago when, in college, for the first time, I heard this

An expert is a man who has made all the mistakes which can be made, in a narrow field.
                                                                                          Niels Bohr (Physicist 1885 – 1962)

Initially I didn’t understand it, but it fascinated me, with time I learned to appreciate it.

Let me demonstrate it for you.

I smoke cigarettes that i roll up by myself and in the years I screwed up in likely every possible way while rolling one, and learned a lot about how to make a cigarette even in the most adverse weather conditions like gale force winds and pouring rain. I never rolled during an earthquake but if I can do it easily while driving a non automatic car in the city traffic, I can infer I can do it if the earth shakes a little so I can exclude this edge case. I can proudly claim to be an expert in the narrow field of “Rolling up cigarettes”

How about domains more complex than rolling up cigarettes?

When we talk about a complex domain, like software testing for example, what is an expert? If we want to go by Bohr’s definition we could assert that an expert in software testing doesn’t exist because it is physically impossible for any human being to make all the possible mistakes in such complex domain in one single life. I tend to think that Bohr’s quote is still valid for complex domains and real experts in such domains don’t exist.

These are what I imagine the 5 stages of expertise to be

As in stage 4, learning is an infinite activity, obviously there will be a wide range of expertise within the same stage and the closer you get to infinity the more you become an expert. Is infinity relative to time? Amount of books read? Number of experiments run? Maybe all of it.

This stupid model has been imagined by me, a person that believes that, in relation to software testing, he is is in stage 4 “Perpetual Learner”.

The reason why you don’t see the 5th stage is thatI haven’t reached it, in fact I don’t even know if such stage exists or not.

On the other hand, if the 5th stage existed, it would invalidate my own very model, in fact the model states that “Learning is an infinite activity” that contradicts the existence of a 5th stage. So should I exclude the existence of a 5th stage, so that my model works? Not really, I’d rather search for the reason that invalidates my model than defend it. Why? Because I learn more when I make mistakes than when I am right, how about you?