Josh Kelly has faced dark times in his career.
His stoppage loss to David Avanesyan was a major setback in his professional career at the time, which has necessitated several solid victories for Kelly to rebuild.
But outside the ring, he has also put himself through the mill with tortuous weight-making. He took his body and mind to extremes.
Kelly told Sky Sports: "At 147lbs it was hard. Even if I'd go out and I'd eat clean, I'd be blowing up to like 175lbs. [I was thinking] How can I make this weight anymore?
"I'd be coming down to maybe 161lbs and boiling down from there to make 147 over one night, it was just crazy. Fifteen or 16lbs was the most I've lost in one sitting, which was hard," he continued.
"I had to get carried up off the bed and everything and I just couldn't even see the opponent in front of us [at the weigh-in]. I was stood there thinking 'I don't even know where I am'. Then you've got to fight 12 rounds after that or 10 rounds or whatever it is."
On one occasion, he revealed: "I thought I was having a heart attack in the bath.
"I could see my heart stop, and I was like 'Why is it not coming back?'
"I had a massive panic [thinking] I can't make weight."
He will fight Liam Smith at middleweight on the undercard of Anthony Joshua vs Daniel Dubois at Wembley Stadium on September 21, live on Sky Sports Box Office.
That's a higher division than Kelly has operated in before, which could favour Smith whose last three fights have been at 160lbs, including his win and his loss against Chris Eubank Jr.
Liverpool's Smith has top-level experience. He's been a world champion before and boxed the likes of Canelo Alvarez and Jaime Munguia as well as Eubank Jr.
He applies aggressive pressure, but does so with a canny boxing mind.
But if he is deemed to be strong in the areas where Kelly is perceived to be weak, then the Sunderland man insists he welcomes that. For Kelly, this moment is an opportunity to prove himself finally and silence his doubters once and for all.
"They don't think I've got no dig and grit, and I tire and stuff like that," Kelly said. "I'd love to be able to take it to the late rounds and prove what I've got.
"I know I can mix it up on the inside and take it to him. Maybe later on in the fight, I'll do that.
"I believe I'm carrying the strength now to take people out.
"It was never physical. It was all mental with me," he added. "I was putting way too much pressure on things.
"In hindsight, I've got one of the strongest mindsets if you think about the stuff I was going through.
"The struggles I've had outside the ring, people don't know about… Fighting's nothing now, fighting's just another day."
Watch Liam Smith vs Josh Kelly on the Anthony Joshua vs Daniel Dubois bill on September 21 live on Sky Sports Box Office.
