Everyone knows that Monaco GP is a lottery and if it rains, we can expect that any body who is lucky on that day can win.
As we saw with Sutil, who was at unbelievable fourth. Thats what will happen, if you try to block a much faster car.
McLaren were lucky with their lottery whereas Ferraris were unlucky. Simply weather played into the hands of McLaren. Lewis mistake turned very lucky for him, as he could get the right tyres at the right time.