Sir Mo Farah will get an idea on Sunday how hard his life as a marathon runner could be -- and whether the doubts he seems to harbour about his new career have foundation.
The Olympic track great will compete in the inaugural Big Half on London's roads as a test of his training in order to establish what work he still needs to do to make an impact in the real thing next month.
If it doesn't go well, the footage he has been watching almost wistfully of the World Indoor Championships in Birmingham may well gnaw away at him; the mood music greeting him before April's London Marathon might contain the odd bum note, too.
There's no reason to think Farah will fail in his goals, of course, even with the big freeze dominating the local build-up to Sunday's 13.1 mile race; even with reigning London Marathon champion Daniel Wanjiru and leading British marathon runner Callum Hawkins -- if the Scot can successfully battle the elements on the drive down from Scotland -- providing stiff competition.
A decent time of an hour or less -- Farah has gone under 60 minutes twice before in half marathons -- and a top-two finish would be very promising. However, he seemed to describe himself as in something akin to road-racing no-man's land during a media conference call Friday.
"Mainly for me it's to test myself, see where I am, enjoy it, go back to the training camp and get ready for [the] London [Marathon]," Farah said.
"I wouldn't be competing if I didn't enjoy it and believe in the sport. Of course, I have [still got the hunger]. You set your target and get through it. It's my first marathon -- if you look at every great marathon runner: Haile Gebrselassie -- his first marathon wasn't a shifter. It's about enjoying it."
Farah, mostly, said the right things on the call, but this was not exactly head-thumping, Mobot-like self-assurance.
He insisted training with new coach Gary Lough, the husband and former trainer of Paul Radcliffe, had gone well in the heat and altitude of Ethiopia, although it had left him tired. He said he had gained some confidence that he might be able to compete at the very top in the marathon; and made racing for Britain on the road in the 2020 Olympics sound like his target, without quite committing to it.
"I need to be mixing it with the guys," Farah said. "It would be hard to just turn up [in 2020] to make up the numbers. Hopefully over the next couple of years I'll understand the marathon and get better at it."
Perhaps it is understandable that Farah is unsure of his prospects since leaving the comfortable glow of success he enjoyed on the track.
When Farah ran the London Marathon in 2014 -- his only competitive race at the distance -- he finished eighth, and for a man who was king of the world at 5,000 metres and 10,000 metres time after time, that rankled.
Finishing nowhere near the podium was an unfamiliar experience, then, and so, too, has been finding himself outside the favourites at his chosen distance. To suddenly be the new, callow kid on the block as his 35th birthday looms, after all he has achieved, must be disconcerting at the very least.
So would he consider a return to the track? "Ask me after two more years!" he joked. "No, definitely. Looking at the World Indoors, you're like hmm, hmm .... Nah.
"You won't see me on the track. I'm going to learn about the marathon and see what I can do in the marathon. I'm done on the track. I've achieved what I wanted to and there's not a lot more I can achieve on the track, unless I just want to go out there and enjoy it.
"I want to build something new and continue on the road."
If there was a theme for Farah on Friday, it was that he was moving on: from the track, from life as a sporting untouchable, and from the controversy that surrounded his former coach Alberto Salazar, with whom there has been no contact while both have been in the UK.
Quite what he will be moving on to is less clear, but racing certainties include much more time back in Ethiopia before the London Marathon, more miles clocked up in training, substantial appearance fees in the future and the dogged pursuit of greatness reclaimed.
When Farah last ran a half-marathon in sub-zero temperatures, in New York four years ago, he was taken away in a wheelchair after collapsing at the end of a race in which he finished second.
This time, with a forecast for an improvement in the weather by Sunday, he said nothing would stop him from taking part. At least in that, he sounded more like the athlete the British public have taken to their hearts.