Maul estava confiante demais e despreparado
Da Novelização da Ameaça Fantasma:
Darth Maul walked slowly to the edge of the melting pit, tattoed face bathed in sweat, eyes wild and bright with joy. The battle was finished. The last Jei was about to be dispatched. He smiled and shifted the remnant of his shattered lightsaber from one hand to the other, savouring the moment.
Eyes fixed on the Sith Lord, Obi-Wan Kenobi went deep inside himself, connecting with the Force he had worked so hard to understanding. Calming himself, stilling the trembling of his heart, and banishing his anger and fear, he called upon the last of his reserves. With clarity of purpose and strength of heart, he launched himself away from the side of the pit and catapulted back toward its lip. Imbued with the power of the Force, he cleared the rim easily, somersaulting behind the Sith Lord in a single smooth, powerful motion. Even as he landed, he was drawing Qui-Gon Jinn's fallen lightsaber to his outstretched hand.
Darth Maul whirled to confront him, shock and rage twisting his red and black face. But before he could act to save himself, Qui-Gon's lightsaber slashed through his chest, burning him with killing fire. The stricken Sith Lord howled in pain and disbelief.
Isso nos dá um pouco mais de detalhes sobre o incidente do que o filme sozinho.
Essencialmente, Maul está sofrendo da fraqueza mais comum e maior do Sith. Como Lucas disse ao imperador,
"Your overconfidence is your weakness."
Maul não está em posição de luta. Ele não está prestando atenção. Ele não está em estado de alerta, ele está convencido de que ele já ganhou e só resta a morte. Ao mesmo tempo, Obi-Wan está sendo tudo que um Jedi deveria ser - calmo, controlado, autoconfiante, sem emoção. Os maiores pontos strongs de um Jedi contra a maior fraqueza de um Sith - e os Jedi venceram.
Vamos lembrar também desta linha de Mark Twain:
The best swordsman in the world doesn't need to fear the second best swordsman in the world; no, the person for him to be afraid of is some ignorant antagonist who has never had a sword in his hand before; he doesn't do the thing he ought to do, and so the expert isn't prepared for him; he does the thing he ought not to do; and often it catches the expert out and ends him on the spot.
Mais uma vez, isso retorna ao excesso de confiança. Maul tinha certeza de que ele superava seu oponente em todos os sentidos, então quando Obi-Wan fez a coisa estúpida e tentou atacar um adversário superior em terreno alto, Maul não estava esperando por isso.