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Three-time Olympic eventing medallist Fox-Pitt, 47, has been named in a 12-strong Team GB equestrian squad for this summer's Games.
He suffered a head trauma when he fell from his horse at the World Young Horse Championships in France in October.
"I felt maybe Rio was selfish but it gave me a kick into action," he said.
"I did think I'd been doing it for 32 years, did I need to carry on doing it?" he told BBC Sport.
But Fox-Pitt, who won Olympic team silver in Athens 2004 and London 2012 and team bronze in Beijing in 2008, said "an individual title would be marvellous".
"I think if I did win a medal my wife would make me give up.
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"I've been around a long time, I'm 47 and I'm hoping my wife thinks this will be my last Olympics. I'm not ruling myself out for Tokyo, if it happens brilliant.
"The Rio goal was a great drive personally, it gave me a good reason to get back", before adding of his ride: "I didn't want to let Chilli Morning down, I put everything into getting selected."
Fox-Pitt was competing at Le Lion-d'Angers when he fell from Reinstated, which was unharmed. "I've come off a lot of times in my life, and in being knocked out my memory has been very selective and I've been able to put it behind me."
He said the fall "affected my sight, my judgement and made me more dozy, in the beginning it was all a little bit of a dream".
"It's been an incredible journey, I've had incredible support."
Meanwhile world, European and Olympic champion Charlotte Dujardin will ride with fellow 2012 gold medallist Carl Hester in the dressage.
London gold medallist Nick Skelton goes to his seventh Games in the jumping.
Another gold medallist in London, Ben Maher, joins Skelton in the jumping team along with Los Angeles 1984 silver medallist John Whitaker, who will be competing in his sixth Games.
Younger brother Michael Whitaker, who also won silver in 1984, is heading to his fifth Olympic Games.
Fox-Pitt is joined in the eventing team by three Olympic debutants in Kitty King, Izzy Taylor and Gemma Tattersall.
There are two Olympic debuts in the dressage as Spencer Wilton and 2015 European team silver medallist Fiona Bigwood earn selection.
Squad:
Eventing: William Fox-Pitt, Kitty King, Gemma Tattersall, Izzy Taylor, reserve: Pippa Funnell MBE
Dressage: Fiona Bigwood, Charlotte Dujardin OBE, Carl Hester MBE, Spencer Wilton, reserve: Lara Griffith
Jumping: Ben Maher MBE, Nick Skelton OBE, John Whitaker MBE, Michael Whitaker, reserve: Jessica Mendoza
William Fox-Pitt says his dream to compete at a fifth Olympics in Rio gave him the "great drive" to recover from a fall and induced coma last year.