There are three ways to win a race. The first is by having the fastest car, the second is by capitalising on the circumstances of the day and the third is by taking advantage of the misfortune of others. Two of them, you can do something about - but the third is in the hands of outside forces and not under your control.
At Spa, Ferrari showed it had the fastest car by locking out the front row. Then, it was about executing the race correctly to take a one-two. But the Mercedes cars proved during practice that they were good on their tyres over longer runs and wouldn't be easy to escape.
Both the Ferrari and Mercedes pitwalls made mistakes. Ferrari's was by pitting Sebastian Vettel very early on lap 15, and Mercedes by pitting Lewis Hamilton on lap 22, which was a couple of laps too late. We're only talking a few laps in either situation, but they did what they did and by lap 27 on the mediums Vettel was saying his tyres were getting past their sell-by date.