Giaccherini joined the Black Cats in a €7.5million deal.
"Leaving Juventus was a very difficult decision to make," he said.
“It was hard because I left many friends, teammates and a Coach in Antonio Conte who made a difference to my career.
"I’m happy with the choice I made though even if I had to give up a top club like Juve.
"I considered a number of factors and not just the economical one. It was a lifestyle choice too, that allows me to play with more regularity."
"A player needs to look inside himself," he added. "Perhaps pride played a part in the move, because I wanted to become a protagonist in a team again.
"Not that I wasn’t at Juventus, because I always looked to contribute when asked to do so, but I wanted to play more often."