Mo Farah has admitted he doubted whether he would be able to continue his global track domination after his ill-fated marathon attempt last year.
The 32-year-old will start his bid for a second gold medal at the World Championships in Beijing on Wednesday when he goes in the heats of the 5,000 metres.
The double Olympic champion has endured a tough year off the track, caught up in the doping allegations against his coach Alberto Salazar, but has been in top form on it.
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He coped with the fast pace set by his Kenyan rivals and a last-lap stumble to take gold over 10,000m two days ago.
It gave him a sixth straight global title and came 16 months after his chastening debut over 26.2 miles at the London Marathon, when he could only finish eighth.
"I never thought I would come back this good, you doubt yourself," said Farah, who bounced back from that setback by winning two golds at the European Championships lasts summer.
"Like the marathon, I thought I would lose speed, I thought I would go there and maybe not come back."
Farah, who last month ran three minutes 28.93 seconds over 1500m in Monaco, the second fastest time ever by a European and one bettered only by himself, added: "This year I have been doing even more quick stuff. It gives me good confidence to run 3:28. It was amazing.
"If I can get into this shape again, next year will be good. It's going to be harder because it is the Olympics and every athlete wants to do well at the Olympics. But if I can continue to do what I am doing, hopefully I will be in similar shape or a little bit better."
Farah believes his achievements can only be fully appreciated by understanding the sheer brutality of the training regime behind his success.
He spends months of the year away from his family in Portland, Oregon, training at altitude in Kenya and the Pyrenees, a sacrifice necessary to get to, and then stay at, the top.
Asked if he was taken for granted, Farah said: "I don't know. It's not easy. I don't blame people, they don't see what it takes.
"I wish sometimes people were there to see you at training, when you are on the floor when you have done back-to-back runs or at high altitude."
And he hinted that it might not be until after his career that his greatness is acknowledged.
He added: "When you step off the track and then you look back, then you kind of think that was great. Like in football, the year when Manchester United had Gary Neville, Beckham, Giggs. They were the greatest, they were unbeatable, when you look back at it.
"Like Arsenal with Bergkamp, Ian Wright, all these guys, you look back and they were legends - or Real Madrid with Zidane or Ronaldo.
"In everything we do, when it's gone, then you look back and learn."