Bonucci was distraught at the final whistle of a 4-0 defeat that ended their Euro 2012 adventure.
"It's a heavy blow. You can lose a Final, but it hurts to lose it like this," he told Rai Sport. "If we had been a different side from the start then we wouldn't have lost 4-0. Spain probably would've won anyway, but we would've made it more difficult for them.
"There was also such bad luck with two thigh strains and no substitutions left, so that knocked the wind out of our sails.
"We came into the tournament off a friendly defeat to Russia, but we showed that we had character. That character was perhaps what was missing tonight, as we reached the Final completely exhausted.
"I think we got the wrong approach from the start, as with a team of this level you can't give them any space."