Experience is certainly about 75% of it, I'd say the other 25% is attitude.
An obsession with attention to detail, patience, and a healthy lack of trust in one's own abilities count for a lot. Add to that a strong desire to keep getting better - whether it's in adding tickets, or learning other people's approaches, or just improving personal skills.
That's my view as a company Chief Engineer (2nd company, 4th year in the role). The one thing I really dislike is Engineers or technicians who qualified years ago, feel comfortable, and just wish to muddle on for as long as it takes to retire - sadly I've had a few, there's not even any point in spiking their interview boards if they go for promotion, you can guarantee from their attitude they won't have done their homework.
G