MEDLAND: Was Rosberg's retirement a shock?

Nico Rosberg walked into the room in Vienna's Hofburg Palace for a press conference as the new F1 drivers' champion, and was just hours away from being officially handed the world title. Now it's a trophy he will receive as a former Formula 1 driver.

The German has been celebrating his first drivers' championship with numerous appearances around the world this week, and it will remain his only title after he shocked all in front of him by announcing his immediate retirement from the sport on Friday.

So why has the man who has only been F1 world champion for five days decided to walk away now?

Rosberg's key stated reason was the commitment he had to make to F1 in order to get the better of teammate Lewis Hamilton. Two title defeats in the last two years had hurt - Austin 12 months ago especially so, Rosberg admitted - and having achieved his childhood dream, suddenly there was no longer a goal worth making so many sacrifices for.

Few drivers get the opportunity to win a world championship, let alone walk away at the very top of the sport. Rosberg took both opportunities when they presented themselves this week.

There were some telling comments from his father Keke Rosberg in the Abu Dhabi paddock, who explained some of the messages he would send to his son ahead of each race.

"You try to keep spirits up and enjoy," Keke said. "It is a sport and it has to be enjoyed. The pressure should always be less than the enjoyment."

It seems the pressure had become the overriding factor for Rosberg in recent months, but he was not going to let it rob him of his chance to win the title first. It was apparently a decision he made quickly, because Rosberg only signed a new contract this year. The first thoughts entered his head after his win in Suzuka, when it was in his own hands to become world champion. It was the light at the end of the tunnel.

Hamilton - somewhat ungraciously - said he was not surprised by Rosberg's decision because it was the first time in 18 years the German had got the better of him to win a title. Perhaps that also played a role, with finally doing so an added satisfaction that Rosberg wanted to prove to himself.

There is also the argument of the length of the season. Mechanics and engineers on race teams up and down the grid have been stepping back from racing all year amid the pressure of an unprecedented 21-race calendar. It's a dream job for so many, but when there are families to think of, it takes a huge toll on personal relationships being away from home so often.

Rosberg himself is father to a one-year-old daughter, and was only married in July 2014. As we're often reminded, Formula 1 is a team sport, and Rosberg is just a key component in a very big organization that aims to win races. Just like any of those less high-profile team members, he, too was having to call on his new family to be extremely supportive, and the 31-year-old felt the time had come to stop asking that of his wife and daughter.

Should we have seen it coming? Sport matters, but there certainly are more important things in life. For fans and observers, you'd imagine Rosberg was on top of the world after his title win - and perhaps he was - but that just meant he had nothing left to conquer.

In hindsight, there was a clear hint from his father following the race on Sunday, as he explained the value he had given to certain achievements in Formula 1.

"I had a rule when I came into Formula 1: you have to win your first race, you have to win Monaco, and you have to win the championship and that's what I said to Nico. Now, he can tick all these off and say 'been there and done that'."

It had appeared Rosberg's overtaking maneuvre on Max Verstappen in Abu Dhabi - which proved so crucial to securing the championship - was his bravest move of the year. That now pales into insignificance in the shadow of what today was perhaps the bravest move of his life.