Even a game as sweet as Toblerone and as efficient as a Swiss watch must get stale and break down eventually.
But just when does Roger Federer reach his use-by date?
The Swiss tennis great has been the world's No 1 player for 266 weeks, won a record 15 grand slam titles, including a breakthrough at last year's French Open and, despite a scare in his first match this week, has eased into the third round at the Australian Open.
The most successful player the world has seen hopes he can hang on for as long as possible, but it's not just age catching up on him.
At 28, tennis statistics are working against him, but so too are a clutch of young contenders who have joined Rafael Nadal as the best batch of challengers to Federer's reign since he first claimed the top ranking in 2004.
Federer and Nadal, 23, have shared 14 of the past 16 grand slam titles, interrupted only by Novak Djokovic in Melbourne in 2008 and Juan Martin del Potro in New York last year.
Andy Murray, the same age as Djokovic at 22 and a year older than del Potro, is loitering just behind, the only member of the top five not to have won a major title.
Russia's late bloomer Nikolay Davydenko bucks the trend also at 28 and has beaten Federer twice in recent months on his way to winning the World Tour Final and Doha events.
But few players have won grand slam titles even after 25, let alone 28.
Andre Agassi is the exception, winning five of his titles from the age of 29, while Federer has so far won six majors after turning 26.
From the age of 28, the results dry up, even for the all-time greats. Pete Sampras won two of his 14 after turning 28, Ivan Lendl claimed two of his eight, Jimmy Connors one, John McEnroe did not add to his seven and Bjorn Borg had retired with 11 grand slam crowns when he was 25.
But dual US Open champion Pat Rafter, who won his two titles aged 26 and 27, believes Federer can cling on for a little longer.
"When you've had as much success as Roger has had, 28 is probably seen as getting old," Rafter said. "But Sampras was 30, 31 when he won the US, Goran [Ivanisevic] as well when he won Wimbledon.
"I think Roger's got two more slams left in him. I hope he does. I'd love to see him win 20."
But Rafter sees the challenge from the other players as being even tougher than the march of time. "It's going to be hard for him, bloody oath. It's not going to be easy.
"Every generation has its depth, but the last two years has really had it. Five of them are vying for it every time and Davydenko probably makes it six."
Federer hopes to fend off the challenges for a while yet. "It's something that you just hope is going to last as long as possible," he said.
"What I've achieved nobody can take away from me. That's obviously something that's very satisfying. It's also something I like doing."
Federer says his new status as father hasn't diminished his hunger to win, but he's now aware he has other commitments since the arrival of twin girls Charlene and Myla last year.
"Where I'm going to spend my vacation, how I'm going to spend time with my family, how I'm going to practise and which tournaments I'm going to play" are all issues he now has to confront, he says.
Much has been said of Federer's new role as father and whether he can handle the pressures fatherhood brings with those required of a grand slam champion.
Father of six McEnroe thinks not.
"There's no tougher opponent than kids," he said before the Australian Open. "When you try to juggle that, try to spend the time necessary to be the best player in the world and be a great father and husband, it gets more complicated.
"When I had kids I thought I could handle both things. My first child was at 27, and I don't remember a whole lot of major wins from 27 on."
But as the figures show, few players have won majors after 27.
And many fathers have coped and succeeded in pressurised jobs. Tony Blair was Prime Minister of Britain when new-born Leo joined his three siblings living at No 11 Downing St - No 10 was too small for a family of six.
Federer is simply enjoying the rhythms of life, including fatherhood.
It's not fatherhood that's going to cut him down, it's the simple fact that fatherhood is accompanied by ageing.
And a gang of four very good, very young tennis players.
- AAP
Tennis: Federer faces twin challenges
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