The Scot says that he and the 19-year-old hotshot didn't always see eye to eye.
Lambert gave Grealish his Villa debut at the start of this season, as the teenage attacker would go on to impress in four league cameos and one cup start, before penning a new long-term deal in October to ward off interest from top-flight rivals.
The Solihull-native seemed primed for a major role in the first-team at the time but instead but spent the next few months either warming the bench or in the reserves while fans clamoured for his inclusion.
However, with Tim Sherwood replacing Lambert at the helm in late-February following his sacking, the 19-year-old has since found his way into the line-up, earning rave reviews from six straight starts and leaving many wondering why the previous regime did not seem to believe he was ready for regular action.
The Scot stresses that he has been delighted to see Grealish performing so well of late but believes that he and his former coaching staff handled his development in the correct manner.
“We didn’t always see eye to eye,” Lambert said on Thursday morning. “He was a young player with a lot of promise but you’re trying to teach him what can happen if things can go wrong – you’re trying to harden him up.
“I’m delighted that he’s doing well now and having a sustainable run but there will come times that he’ll find it hard and things don’t go his way.
“He’s playing without fear, as a young player always does. We took him to America [for preason] and let him see how a pro lives and they actually do it.
“And we gave him his debut and, to be fair to him, he’s doing well.”
Grealish's recent emergence has also led to an international tug-of-war, with the Republic of Ireland Under-21 midfielder refusing a first senior call-up this week amid speculation that he is considering switching to England.
The decision has seen him come in for criticism from some quarters and Lambert believes that he has now put himself in a tough spot.
“It’s a hard one,” the former midfielder said. “There was a time when I was there when the Irish Under-21s were going to call him up and he never wanted to go there with them.
“Maybe he’s waiting for England? – I don’t know, but it’s his choice where he wants to go.”