#4 Experience
With 76 Grand Prix starts between 2006 and 2010, Kubica is an experienced driver, not to mention his time racing in other series. He's 34 years old now, which may seem a bit on the elderly side, but that's the same age as Hamilton and the Englishman is currently in the form of his life.
Of the current drivers, only Raikkonen is older than Kubica and in terms of races competed in, he's around midtable, despite the much longer seasons in recent years.
To expect Kubica to hit the ground running and get good results immediately is unrealistic, however, as the old saying goes, form is temporary, class is permanent. Given what we've seen from him in an F1 car so far, there's a definite cause for optimism.
Kubica could've already been a world champion if his BMW team kept developing their car to the end of 2008, one of the worst decisions in recent times.
Many great drivers have come back from hiatus and not been the same force as they once were, but the fire is still burning inside Kubica, that's clear to see from his interviews.