"But there were too many messy situations and I couldn't do it anymore."
The 35-year-old was given a lukewarm reception by new club Atalanta after signing on a free transfer this summer as fans felt he betrayed the Orobici by leaving for Tuscany last summer.
"People don't always know the reasons behind a certain choice," Vieri insisted. "I returned to Bergamo because my heart told me to. I will convince the fans by playing well.
"I have always played because I enjoy it and the money is a secondary consideration. It used to matter a lot, but now it hardly does. I signed a blank contract with no figure on it.
"Football is my life - it's my adrenaline. When I have the ball I am happy."