You’re one of the very best in your chosen field. You have always excelled. Your perfect record is beyond reproach. You’ve risen to every challenge and done everything asked of you.

Suddenly a new challenge emerges and the word is you have absolutely no chance of succeeding.

When unbeaten IBF welterweight titleholder Kell Brook enters the ring at the O2 Arena in London, England, and patiently awaits the arrival of the fearsome IBF, WBA and WBC middleweight titleholder Gennady Golovkin, the atmosphere will be akin to that of a hanging for the majority of fight fans around the world this Saturday.

Thankfully, Brook, who is currently rated No. 1 by THE RING at welterweight, has an entirely different mindset and insists that naysayers simply come with the territory.

“I’ve always been after major fights,” said the Sheffield-born challenger. “I’ve said, from a very early age, that I’ll win world titles from welterweight to middleweight and now I’ve made this jump to 160 pounds and here we are.

“A lot of people are writing me off but I’ve been in this game for a long time and everyone has an opinion. I understand that I’m moving up two weight divisions and that I’m going in against a great fighter but that is what excites me and that is why I love this fight. To be the best, you’ve got to beat the best and people are going to be very surprised by my size, my speed, my strength and my skills. I’m going to a completely new animal and I’m looking forward to showing the world what I can do as a middleweight.”

The size disparity is one reason Brook (36-0, 25 knockouts) has been installed as a 5/1 underdog to become the first reigning welterweight titleholder to win the middleweight crown in 50 years.

Emile Griffith achieved the feat when he outpointed Dick Tiger at New York’s Madison Square Garden on April 25, 1966, and it has never been done since. Griffith weighed in just over the welterweight limit at 150.5 pounds, while Tiger came in at a full 160.

Brook, conversely, is undergoing a physical metamorphosis and will be a full-blown middleweight when he hits the scales. “I’ve been lifting the weights, building muscle, eating good and, more importantly, I’ve been doing all the hard work in the gym,” he explained. “Even though we’ve been lifting weights, we’ve been retaining the speed, while increasing the power and the strength.

“We’ve brought science into our training and everything has been measured. We’ve been moving weight, moving it fast, going through numbers and hitting targets. All of this is calculated towards working the right muscle groups, so that everything is efficient for me in this fight. The people I work with know all the science behind it and I just go in there and get down to work. I put my trust in the team and they push me hard.”

“The Special One” trains out of the acclaimed Ingle Gym in Sheffield, which has been churning out champions for decades. It is scandalous to suggest, as many have, that a world-class operator like Brook is cashing out and knows he can’t win. Fighters by nature are gamblers and risk their lives every time they step into a prize ring and that is a difficult proposition for the average person to truly understand.

The 30-year-old Brook was quick to point out Golovkin’s qualities but left no doubt as to his intentions of testing the champion to the full.

“(Golovkin) cuts the ring off well and generates terrific power,” said the challenger. “I’ve asked people who I respect in the game to give me something negative and there’s really nothing you can say. Win, lose or draw, I know I’m going in there with the best fighter in world boxing.

“A lot of people said that I didn’t fancy taking on the best fighters but all those doubters know now that I’m not f__king about. I’m in there to give the fans the best fights possible. This was the biggest fight I could have taken at this point in my career and what a fight it is.”

So, if Brook were to prevail, would it be the greatest win ever by a British fighter?

“Absolutely, it would be up there. Can you name anything bigger?” asked Brook inquisitively.

This reporter brought up Randy Turpin outpointing Sugar Ray Robinson in London in 1951 and Lloyd Honeyghan stopping Donald Curry in Atlantic City in 1986. Both were monumental upsets of a similar motif; however, it must be mentioned that Turpin and Honeyghan were throwing down against brilliant champions in their own weight class.

Golovkin (35-0, 32 KOs) may very well be an all-time-great when his own career is over. His ascent to the top has been very similar to Mike Tyson’s peak years, when top contenders were being spectacularly knocked out for fun. As it turned out, Tyson’s flaw was a lack of discipline but this reporter was keen to know what flaw Brook had detected in Golovkin.

It’s a rare occurrence but the 34-year-old Golovkin has switched off and been caught in fights and he also has the tendency to back up in straight lines.

“That’s very accurate,” said Brook immediately. “He leaves himself there to be hit, at times, and I’m going to hit him very hard. He does seem to have a good chin and walks straight through these fighters but I’m going to bring speed, head movement and my boxing brain. The plan is to hit and not be hit.”

It all sounds fantastic but 12 rounds is a long time. Ever since the fight was announced, this reporter has felt that Brook would give Golovkin the fight of his life. You never write off quality and that is exactly what the challenger brings to the table. But can he really pull off the victory?

Brook has so much against him on Saturday but still talks with the self-assuredness of a top professional who knows precisely what he’s doing.

“I will be victorious at the end of the night,” he said. “If the knockout comes, you know I’m going to take it – that’s always the plan. This fight means everything to me and there’s a lot at stake. I’m unbeaten and I’m in it to win it. I’m not coming to make up the numbers. I’ll be there to rip those titles off of him.

“This is the sport I love and I’ve put my whole life into it. I just can’t put into words what it will mean to go down as a serious legend and be talked about for years and years and years to come.”

Tom Gray is a UK Correspondent/ Editor for RingTV.com and a member of THE RING ratings panel.  Follow him on Twitter @Tom_Gray_Boxing