Hartley, who made his grand prix debut this year and will race for Toro Rosso full-time next season, was dropped by Red Bull during 2010 having been its reserve driver.
Hartley, speaking in an interview in the latest episode of Motorsport.tv programme The Flying Lap, accepts he wasn't experienced enough for that first opportunity.
"I wasn't ready at that point," says Hartley. "I have big respect for the likes of Max [Verstappen], who has come in at the age that I was.
"I had a real opportunity to be there, but when it came down to it I didn't have all the experience that I needed and maybe support and I crumbled when I shouldn't have."
Hartley believes he is a "more rounded" driver today for the experience, having enjoyed a successful sportscar career with Porsche.
"I learned a lot from that and I feel like I'm a lot more rounded driver today than I ever could have been at 18," says Hartley.
"The timing has been perfect and I think you keep on improving. I had a tough time, but it was also important for me to learn from."
Source : https://www.motorsport.com/f1/news/hartley-crumbled-on-first-formula-a-shot-987686/