Monza was tragic for Ferrari. It all looked so good, the front row in the starting grid belonged to Raikkonen and Vettel, so the Grand Prix promised a fat bounty for the Reds. But it went so very different.
Hamilton had promised he would "try everything" to win this, and he literally did just taht, right from the start. But in the corners 4 and 5, a left/right combination (Variante della Roggia), Hamilton, third, behind Vettel, pushed in, around the outside, and, when he was slightly in front, coming into the second part of that combination, he was on the ideal path, and Vettel had to decide:
Do I go a more outside way, leaving my biggest opponent to go ahead in front of me, who HAS to win the italian GP...
Or do I push back in and try to stay head to head with Hamilton?
Vettel chose #2, and he chose wrong. Both cars touiched, but, not a surprise, the inside car has the advantadge, and the outside car, the Ferrari, was spun around and had to let the field pass, being in 18th position now, with a damaged body.
That was the key situation