The great thing about longbows vs armoured knights was that, while a longbow couldn't penetrate armour as a crossbow did, a few well-placed shafts were quite enough to persuade even the best-trained destrier that it would rather be somewhere else, and to head off there rapidly, having rid itself of its troublesome rider! An armoured knight on foot is still formidable, of course, but lacks the ability to perform the devastating charges that could break enemy lines.