Mario Mandzukic did not always have the strength to out-muscle a defender. As a kid, he was actually on the small side - so much so that some adults even told him he lacked the stature to play on the wing.
Of course, he did not listen. Instead Mandzukic focused on those things he could control: his work rate, his stamina, his speed. At 11 years old, he ran an astonishing 3.3 km (2.05 miles) in the Cooper Test - a military-conceived drill, in which participants are challenged to go as far as they can in 12 minutes. At 30, his legs have carried him into a second Champions League final.
"It’s not enough to wear the shirt and wait for others to fall at our feet," Mandzukic had warned in an interview with Corriere della Sera last December.
"We need to be ferocious beasts. That’s how you win. And keep on winning."
Nobody has embodied the spirit of those words better than the man who uttered them. Mandzukic was supposed to be the odd man out at Juventus this season, a player with no obvious place in the side following the arrival of Gonzalo Higuain to play alongside Paulo Dybala up front.
The newspapers suggested he might leave. Instead, on Tuesday, he scored the goal that killed off Monaco's last hopes of an unlikely semi-final comeback in Turin.
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For a few hairy moments it had seemed as though Juventus might have forgotten that obligation to battle through to the end. The Italian side dithered through the opening exchanges, giving up a corner in the first minute before Gigi Buffon misjudged the flight of the ball and fell clumsily into Radamel Falcao from the ensuing delivery. Kylian Mbappe hit the post soon afterwards from an offside position.
With a 2-0 lead from the first leg, Juventus was never exactly in trouble. Equally, though, it was hardly desirable to offer such encouragement against an opponent who had scored three or more goals in 27 separate matches already this season.
Mandzukic blew his first chance to kill off the tie, firing too close to his compatriot Danijel Subasic when sent through on goal by Higuain. But he made amends in the 33rd minute, following up on his own parried header to force the ball home at the back post.
It was only his second goal of this Champions League campaign - and his ninth in all competitions - but none should doubt his importance in keeping Juventus on track for a treble. His furious pressing of opponents from the left side of the attack has been one of the many underestimated components in Juventus' charge through this tournament.
As brilliant as Leonardo Bonucci, Giorgio Chiellini and Buffon might be, clean sheets are not truly earned by defenders alone. If the Bianconeri were able to go 689 minutes without conceding prior to Mbappe's eventual consolation strike here, then it is in large part because they made sure that the ball rarely got close to their goal in the first place.
Nor has Mandzukic been afraid to track back when necessary, either. Higuain ought to have made it 2-0 to Juventus in the 37th minute against Monaco, after the Croatian released him with a 60-yard pass delivered from the edge of his own penalty area.
That same stamina which Mandzukic cultivated as a boy serves now to make him a brilliantly flexible weapon in Allegri's arsenal, dropping back into midfield at times and leading the line at others. For a manager whose formations shift constantly with changes of possession, versatility is always an asset.
But perhaps there is even more than this to be said for Mandzukic.
He, like Dani Alves - who scored a goal of his own on Tuesday - has been here and done this before. For a team that is still reacquainting itself with the business end of this competition to have past winners on board is something we ought not to underestimate.
Indeed, that experience might help to explain why it was so easy for Mandzukic to adjust to Higuain's arrival in the first place. This is a man who knows the value of a deep squad. When asked by Corriere whether the Argentinian's arrival had ever worried him, his response was one of blunt bemusement.
"No. Only the strongest players come to a team like Juve," he replied. "I never posed myself the problem [of how we would play together] or made some kind of film in my head … I have a vision of football in which you need to be open to different possibilities, without making too many problems for yourself. You work to win."
And then, you work to keep on winning.
Mandzukic the tireless runner has helped Juventus to reach a second Champions League final in three years. But there is still one tall hurdle left to clear if Juve is to make sure that this one, unlike the last, ends in success.