Disclaimer: FMA belongs to Arakawa Hiromu
Thirty-nine: Sly person
When Mustang considered himself an intelligent – cunning, even – man, he could be considered pompous and proud, but by any modern standard, he would still be correct. He was smart, and knew many things more than other people his age, both theoretical and practical. He knew how to start (and finish!) the alchemical reaction for fixing broken plates; he knew how to manoeuvre an enemy target into a trap; he knew how to instil fear or courage into the hearts of men with a well-delivered speech; he knew how to get important information by, under the noses of his rivals.
But despite all that he could do with his cunning mind, there was one thing he did not yet know how to do. Roy Mustang could not say 'no' to Riza Hawkeye. It wasn't that he was physically incapable of the act – in fact, he'd said the word, and several derivatives of it more than once to her – but rather that whenever he tried to foist off a task she had for him, or wheedle his way out of a sticky situation, he'd always find himself doing just as she wished, however reluctantly he might have done it.
Completing paperwork, taking Hayate for a walk, letting her put herself in danger – it was all the same. She just wouldn't take "No" for an answer, and for that reason, Mustang realised he couldn't be as cunning as he thought himself. Or perhaps it was just that as compared to her mind, he was still a child.