Flying, driving, motorcycling... any skill, especially involving a motor vehicle of any sort, is something that you will never stop learning.
I'd agree with Wayne about a number of people having peak performance at their checkride. What I also see is people who learn more details about flying and become better in certain aspects of flying, but then lose practice for other (critical) aspects of flying.
Example: The instrument pilot who's very good on the radio, but cant hand fly an approach for **** because (s)he uses the autopilot all the time.
You will always have stupid little mistakes happen, just like the rest of us. The catch is checking yourself consistently and giving yourself enough margin that you catch the mistake before it becomes a major problem.
As an example, the other day I departed from a field without a functioning AWOS. So I set my altimeter on departure to field elevation (which is 700 MSL). It was about OVC002, with terrain around, so I flew the departure procedure with a good climb rate. Get into the clouds, and realize that I'm passing 2000 MSL awfully quickly. Oh, right, I set the field elevation to 1700 MSL. Reset the altimeter, and was shortly thereafter talking to Center, who gave me the local altimeter. It was a non-issue in this case because I was going to be climbing well above all obstacles anyway, kept an aggressive climb rate, and realized that there was a problem early on. My co-pilot made the same mistake, too, so it wasn't an isolated pilot failure.
That same mistake killed a plane load of people in a 310 up in Canada in the fall of 2010 in a CFIT crash. Fortunately, I wasn't fly that 310. Many others have suffered the fate of CFIT because of an altimeter that was set 1" off. Since it was a flight between non-towered fields with no AWOS up in that area, flying at night, I'd bet that they departed with the same error, the pilot didn't realize that there was an issue with the altimeter setting, and it didn't cause an issue until he went to land. Better believe I learned something.