User blog comment:Imhungry4444/How strong is he really?/@comment-3202520-20110720095952/@comment-3387274-20110721072823

pure brute force isn't going to work on Haki. Thepowers are predicting attacks, converting will power to "armour" and sometimes a concussive mental blast.

you can't beat an attack prediction with pure brute force, becuase they see it coming and dive out the way. Luffy won with speed, but the other apporaches are to ensure the opponent can't dodge (against Satori), or Zoro managed to do it by launching an attack that even he didn't know the outcome of (by aiming at Ohm through a wall).

In theory another approach would be to hit a very wide area, so they haven't got anywhere to dodge to.

for overcoming the "armour", You could in theory beat it with your own will power, if you had some way of focussing it, and haki is one example of this, but there may be others. mental blasts is just a matter of being strong willed

So haki gives a major advantage, but it isn't impossible to beat a haki user without it.