Attacks from the sides or behind are more likely to hit (both are usually effective unless the target has a shield or the Weapon Guard ability). Shield and Weapon Guard 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 Weapon Guard is equipped). Attacks from the side ignore Class Evasion, and Attacks from behind ignore Class, Shield, AND Weapon Evasion, leaving only Accessory Evasion. Blade Grasp is separate from all this, factored before standard evasion (the game makes a check against Blade Grasp first, with the success% being equal to the character's Brave, THEN calculates against all remaining evasion types that are appropriate for the situation).
But Reaction Abilities like Blade Grasp only work on the first attack, so if you've got the Two Swords ability, the second swing will have a far greater chance of hitting. In fact, against a high-Brave character with Blade Grasp, this is virtually the only way to succeed with a physical attack.