Attacks from the sides or behind are more likely to hit (both are usually effective unless the target has a shield or the Parry ability). Shield and Parry in combination can make attacks from the front all but pointless. Shirahadori/Blade Grasp and a Featherweave Cloak can make even back attacks unlikely at a twelve percent success rate.
Specifically, attacks from the front have to deal with all 4 types of Evasion in a character's stats (Class, Shield, and Accessory Evasion, as well as Weapon Evasion if Parry is equipped). Attacks from the side ignore Class Evasion, and Attacks from behind ignore Class, Shield, AND Weapon Evasion, leaving only Accessory Evasion. Shirahadori is separate from all this, factored before standard evasion (the game makes a check against Shirahadori first, with the success% being equal to the character's Bravery, THEN calculates against all remaining evasion types that are appropriate for the situation).
But Reaction Abilities like Shirahadori only work on the first attack, so if you've got the Dual Wield ability, the second swing will have a far greater chance of hitting. In fact, against a high-Bravery character with Shirahadori, this is virtually the only way to succeed with a physical attack.
Unless, of course, the Reaction Ability is Hamedo/First Strike, which will cancel the attack whether the attacker has Dual Wield or not Brave% of the time.