Radak: Hashem gave it Gevurah - "ha'Siten la'Sus Gevurah"?! Hashem gave it, and when He does not desire its Gevurah, it stumbles and does not save its rider.

Malbim: All preparations will not help [against Hashem's desire]. Not only will the horse not give victory - it will not even save its rider via its strength. Sometimes it brings its rider into the war (front line) against his will!