Hart made his first competitive appearance for the Three Lions on Friday and produced a superb performance to ensure a clean sheet in the 4-0 Euro 2012 romp over Bulgaria at Wembley.
The display has led many to question why the 23-year-old was not called upon when England were having so many goalkeeping difficulties in South Africa, Capello having chosen Hart as his third choice, behind Robert Green and David James.
Yet the Italian's link with Hart goes back two years further.
The Manchester City star was actually handed his England debut in a summer friendly against Trinidad & Tobago, which was the start of an intense period which also saw him become first choice for his club until Shay Given arrived to ease Hart out of the frame.
It took a season on loan at Birmingham to catapult Hart back into the Three Lions picture, and also back into the City team at Given's expense.
And Capello concedes the youngster's attitude now is far removed from what it was.
"I remember when I selected him two years ago he was not the same player," said the England boss.
"He did not have the same focus on games or training.
"He probably started to play in the first XI too early. He started to think 'I am the best'.
"You have to understand what happens in the mind of the young player. Sometimes it is this. But in two years he has come back."
Capello was never seriously worried about Hart's progression.
He always felt the edge to the keeper's attitude would ease with age.
What he was more interested in was the former Shrewsbury man's ability, which he felt was beyond question.
Still, progression has been swift.
Even last October, when Green had been sent off and James then suffered an injury after being introduced as a substitute in the Ukraine, Hart was overlooked.
He might have been in the original squad but when Ben Foster was called up as cover, Hart then had to stand by as the then Manchester United player was catapulted into the England starting line-up.
When Foster subsequently fell out of favour at Old Trafford, Hart was back in the queue, although impressive pre-tournament appearances against Mexio and Japan failed to get him any World Cup game time in South Africa.
However, that lack of action meant he felt able to return to duty quicker than expected with Manchester City.
More encouraging signs during City's pre-season tour of the United States led to Roberto Mancini selecting him above Given for the opening day trip to Tottenham, by which time Capello had already decided Hart would be his first-choice with England too.
"Joe Hart is a really good keeper," said Capello.
"He improved a lot last year when he played at Birmingham. That was a really important period for him.
"With any young player, the most important thing is his quality
"Now it is really up to him."