But when jockeys lose focus and gain weight the doors close quickly. For a 21-year-old Harris the doors closed completely.
He was disqualified for skipping a recreational drug test, which admittedly would have come back positive, and for one reason or another missed five years of race riding.
"I moved to Melbourne and did landscaping because I wasn't allowed to work with horses," says the now 31-year-old.
"And for the first year I never missed racing at all. But then I started to miss it quite badly and it got worse.
"It is all I know and eventually I missed everything about it so I came home to start making my way back."
The problem was Harris was 78kg, a weight at which he felt like a "useless piece of s**t".
"I hated being that weight. It hated how I felt and I had to get rid of it."
Among those who helped was Cambridge trainer Shane Crawford who suggested a vegan diet.
"He was right, that was a huge help and while I am not a vegan anymore it got me back to work."
Plenty of others have helped. Te Akau's David Ellis insists Harris stays healthy and fit while Harris's manager Dean Williams is one of the bright young lights coming through the training ranks as stable foreman for Tony Pike. "Dean is great because he is a people person and knows everybody. And he helps manage when I ride. I can't ride at every meeting because the wasting gets too much."
What also helps is having Catalyst as his potential flagbearer and a pick-up ride like Kali in the 1000 Guineas next Saturday.
Harris loves Catalyst almost as much as punters who will have to cop $1.20 about him winning the $500,000 Guineas today.
"He is amazing to ride," says Troy.
"On most horses when they are going fast you can feel them trying and straining, because they have to.
"But he just cruises it. You don't even know how fast you are going. Yet he is really quiet and easy to get on with.
"I am thrilled to be on him and to get on Kali for next week because I have ridden her a few times this week and she is flying.
"But I am hoping Catalyst is the horse who can give me the boost I need, to put my name in front of people.
"I'd love to be able to ride him in Australia if he goes there."
Opponents like Harlech, Callsign Mav and Sherwood Forest won't just gift Catalyst the Guineas today but unless he performs below the level of his last three starts he should win.
Harris expects a text from his famous father today but no deep instruction. "We don't talk about that sort of stuff very often but he will wish me good luck."
In reality for Troy, who will still need to trim a kilogram in the sauna today to ride Catalyst, most of the really hard work is done. He knows now what his 20-year-old self couldn't. "I know what works for me and how I have to behave and treat my body to be able to do the job.
"When you first start out riding winners you think that is all there is to it. But I found out there is a lot more to it."
Red hot favourite
• Catalyst is one of the hottest classic favourites in recent racing history.
• Victory in today's 2000 Guineas would be the highlight of Clayton Chipperfield's blossoming training career.
• It would also cap an incredible comeback for rider Troy Harris.
• The Guineas is the highlight of the first day of New Zealand Cup week.
