Amir Khan has a quirk.

Whenever an opponent lands a sustained assault, Khan taps his gloves together before retaliating. It is instinctive, but also a sign of his mindset, the reaction that has been stirred within his fighting spirit. For his opponent, it provides a warning, yet Freddie Roach, Khan's trainer, has abandoned trying to eradicate it; he acknowledges it as something involuntary.

The habit might also be recognised as the moment when Khan is at his most unselfconscious and unrehearsed: riled, belligerent, dynamic, he acts like a warrior. This sense of himself, as a combative, natural fighter, is central to Khan. He often talks about tracing his family heritage back to a warrior tribe and he revels in the moments during a fight when he becomes engaged in a brawl; toe-to-toe, landing and taking punches, proving himself to be unflinching.

Yet this intrepidness is a weakness as much as a strength, a contradiction that explains his defeat to Lamont Peterson in the early hours of last Sunday morning in Washington DC as much as the curious officiating of the referee, Joseph Cooper, and queries about the scorecards. Looking back on notes made before the fight, two comments seemed even more relevant. Khan had said he wanted to "win convincingly", while Roach had admitted cautioning against his willingness to lean back on the ropes and absorb blows.

The first remark is a reflection of Khan's growing showmanship. After taking punches from Peterson – a strong, aggressive, streetwise boxer – Khan dropped his arms, as if to emphasise that he was unhurt. It was taunting, though, and reckless. Outside the ring, he is an unassuming trainer, happy to prepare for fights on the road with Roach as he shares his time between the Englishman and Manny Pacquiao. The trainer also describes Khan as an avid listener, willing to learn and be taught. Yet inside the ring, he has a weakness for being occasionally extravagant.

Khan has generated hype in America, where he is promoted as the rising star, the inheritor of the mantle of greatness currently held by Pacquiao and Floyd Mayweather junior. Neither would have lost to a fighter such as Peterson, however gritty and uncompromising the American was. Golden Boy Promotions are a slick and canny organisation, and they will wring every last cent of earning potential out of Khan, but he needs to leave the grandstanding to them.

Khan still behaves impulsively at times in the ring and it undermines the improvements made by Roach, who has worked on his footwork, defence and tactical awareness. In his heart, where the only voice that exists is his own, Khan still considers himself a fearless, vehement fighter, and he too readily succumbs to that impetuosity. His strength, the gift that can make him irrepressible, is his speed; he can hit and move, landing bewildering combinations that overwhelm the resolve of opponents, but is too willing to indulge in a scrap. There remains a psychological barrier for Khan to overcome.

The Peterson fight demanded discipline and professionalism, yet he fell back on the ropes too often. It is a form of machismo, an assertion that he cannot be overcome, but it allowed the American to land several jarring body shots and added to the sense of Khan not being in complete command. Roach had told him to stay quick on his feet, to move out of danger, yet Khan still fought bullheadedly. "He likes to test himself," Roach said. "He chose the wrong tactics."

The observation suggests Khan ignored his trainer's instructions, which tells of a headstrong nature. In fights against dangerous opponents, particularly in their hometown, the smallest margins can be critical, as Khan discovered. Many observers felt that he received a generous count when Willie Limond knocked him to the canvas at the 02 Arena in October 2007, but Cooper's performance was unusual as he docked Khan two points for pushing, an offence that is seldom, if ever, so heavily punished.

The Englishman has cause to complain that a referee who does not regularly officiate at such a prominent level took charge of this contest. Yet he might also question his own indiscipline. Fighting in Peterson's hometown, Khan had to expect his rival would be favoured – though not so significantly – and having been docked one point for pushing, he should not have committed the same offence in the final round. He was not canny enough, not self-possessed enough, to survive the contest.

It was not a devastating outcome, with his promoters and TV channel HBO already anticipating greater interest in Khan's comeback, as a story of redemption that will capture American hearts. Khan will still prosper, but the illustriousness he craves, the status of Pacquiao and Mayweather, demands that he learn some harsh lessons. The great champions win, whatever the circumstances and whatever it demands of them.