Poor Byleth and Shez: each of them says they lost to the other, and they’re not really wrong.
Byleth, as a permanent member of a large crew, sees each battle in a similar way to the lords/other officers: as part of a larger campaign/career. They’ve got Jeralt to deal with negotiations and make sure the client doesn’t stiff them for a job well done—so even if they get trounced on a personal level, they’d know the overall objectives and stuff are what matters. And Shez, being able to hit hard and fast out of nowhere, keeps making them fail those objectives.
“Why? Your job was to stop us, and you failed.”
— Byleth to Shez, after their very first fight
“We’ve faced you in battle many times, only to be bested at every turn.”
— Byleth to Shez & lord, after a fight that hinged on not engaging them
It’s tempting (and funny) to see Shez as too stupid or impulsive to even be thinking about objectives over hitting the enemy with swords, but that doesn’t hold much water. Their stage intro barks are usually about whatever the objective is: rescue, fighting retreat, etc. In SB chapter 7, they’re the one to suggest sidestepping the Ashen Demon by going through Claude. When the chips are down, they’re thinking about what matters—but once the battle’s over, they berate themselves about losing to the Ashen Demon once more.
Which makes perfect sense: after the battle is when pay gets doled out, and when the client might decide to keep you on or cut you off—if there’s a next job, anyway. It’s when you get a sense of how good of an impression you left, which matters for your career. Shez is thinking longer-term—but they tended to move from crew to crew without much attachment, or work solo jobs. They aren’t getting paid to think: that’s gonna be the job of whatever existing force they got hired to work alongside. Objectives matter—you can’t lose the battle—but putting in a strong showing on an individual level matters just as much if not more.
“Sure, we [accomplished every single objective], but other than that, I lost in basically every way you can lose.”
— Shez, to themselves and Arval
“My accomplishments won’t matter if I’m not still standing at the end of the battle.”
— Shez, when performing exceptionally
Shez, who feels a vestigial need to be the best fighter on the field, can’t quite beat the Ashen Demon one-on-one. Byleth, who’s often had the (relative) luxury of focusing on their overall performance, sees Shez as a threat they’ve failed to lock down again and again.
And then we get their chat after Scarlet Blaze/Golden Wildfire chapter 14. Byleth immediately compliments Shez’s strength, and Shez happily points out that without Byleth, Jeralt, and their crew that the battle would have been hell. They get each other, and they know how to make each other feel appreciated once the dust’s settled.