The Turin outfit led 1-0 after five minutes only to concede two goals in 13 minutes before half-time and slip to a 2-1 defeat.
"This defeat must make us reflect," Ventura told Gazzetta dello Sport. "We were in control, we were dominating possession, we were 1-0 up and we had many chances to kill the game off.
"We threw away the game in 13 minutes and I hope this will be a lesson to my players.
"Football is like this and you cannot rule out anything.
"You always have to give 100 per cent."
The loss was Torino's first at home in Serie A since September 29 and dropped the Granata to eighth place in the Serie A table.
Torino are next in action when they travel to Verona to face Hellas February 17.