Three division world champion 'Sugar' Shane Mosley knows exactly what it's like to make the jump from lightweight to face a bigger welterweight.
Mosley jumped from lightweight to welterweight in 1999, and less than a year later he was fighting Oscar De La Hoya for the WBC welterweight title.
Mosley would win a twelve round split decision and many experts labeled him as the best pound-for-pound fighter in the world.
Now Mikey Garcia (39-0, 30 KOs), a four division world champion, is looking to make a similar move by jumping from 135 to 147 to challenge IBF welterweight champion Errol Spence.
Unlike Mosley, Garcia has competed at junior welterweight - where he captured the IBF world title and gained dominant wins over Sergey Lipinets and Adrien Broner.
But Mosley was physically a bigger fighter than Garcia, and Spence is a very big welterweight.
"I think that what he sees is that Errol Spence is probably not as experienced or knowledgable in the boxing game as he is but he has to understand that he's the smaller man and way smaller than Errol Spence," Mosley said to Brian Campbell of CBS Sports.
"The little mistakes that Errol Spence might have is not going to do away with his size. Plus, he has speed and power as well and Spence has been in the ring a lot of times with Floyd Mayweather [sparring] and other fighters so he has experience as well."
Also, Mosley explained that he was a bigger fighter than De La Hoya in the amateurs - whereas Garcia began his career at the featherweight limit of 126-pounds.
He believes the size and power of Spence - combined with his skill - will be too much of a mountain to climb for Garcia.
"I think the difference is I was a bigger lightweight going up to welterweight than Mikey was. Mikey came from like 126 or 122 pounds and now to go to 147. I think it's going to be too hard for him to make that jump if he wants to stay undefeated. I really wanted to go straight to Oscar because when I was coming up, Oscar was actually lighter than me as an amateur," Mosley said.
"He fought at 132 pounds and I fought at 139 pounds in the amateur rankings. With Mikey, it's a little different. He's fighting a guy at 147 who could really fight at 160. It's a different thing. Oscar was obviously a good fighter at 160 but he's really not a big fighter like that. Mikey fighting Spence is fearless but also probably stupidity. I knew I could beat Oscar. We were built similar in terms of weight and other stuff like speed and power. It was a great fight and we were both equally matched and we gave the fans what they wanted to see."