Again, riding a bike is about being able to stay upright. Not exactly the halmark of proficiency. One tends to overestimate one's self; it's human nature.
Simply because fifteen years later one can still remain upright doesn't mean one has remained proficient. Or that one has retained anything of significance.
I spent two years away from the cockpit, and before I took that hiatus, I was very connected to my flying. I thought, the airplane did. It was an extension of me. When I returned, I thought one thing, the airplane did another.
Even muscle memory fades. The ability to judge height in a flare fades. Airspeed control fades. It may be easier to bring back for some, than others, but it definitely fades.
We see a number of individuals who want to upgrade from the flight engineer seat to the right seat, who don't make the upgrade. They have to meet minimum company upgrade requirements in terms of flying experience, and many of them will go rent a simulator for a few hours before coming to class. Even though they may have thousands of hours in type as a flight engineer, they're often our of practice as pilots. For those that are flying privately on the side, it's still a big leap. I've seen a number of them wash out, and it's not because they're not bright, sharp individuals; they are. It's not because they don't know the airplane like the back of their hand. They do. It's because the longer they've spent manning the panel, the lower their proficiency has become, and it shows up when they get in the simulator and have to fly. Even after spending twelve hundred dollars an hour to rent a sim to try to get up to speed before hand, I've seen them wash out because they couldn't fly the airplane.
We've had a number of individuals who did make the leap, of course, but regardless I think every one of them will agree that the level of proficiency drops substantially when not flying, or when not flying enough.
The dangerous ones are those who don't recognize this important truth.