Have you read the article, or simply the title?
"Similarly, your warrior character is not looking over a table of hundreds of weapons, comparing speed factors, damage ranges, weights, costs, lengths and ranges, etc. He wouldn't be able to pick the best handful of weapons to become proficient in either, and even if he could, chances are it's more realistic he learns the weapon his master or mentor happens to be skilled with - or maybe even the weapon he can afford. After all, why do you think they have hundreds of weapons if one were clearly the best?
Yes, the player may pick his weapon as a matter of choice, but when he begins to build upon it using every rule in the book, as if the character had such precise, quantified knowledge, then it is mini-maxing. For example, playing a warrior, specializing in darts - as he has exceptional strength and knows he gets full damage bonuses for every thrown weapon, no matter how unrealistic that is - using racial advantages on top of that, using kit advantages on top of that, etc. etc., will give you a character with such combat bonuses such that he'd be a true wonder of the world. That is a good way to maximize your character's power before they even step out the door and see what color the sky is, but it is not roleplaying.
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At this time I must point out that mini-maxing does not mean you cannot play the role of such a powerful character, and even roleplay it well. A mini-maxer may be able to roleplay very well. In fact, as long as they have a powerful character, they may be excellent roleplayers. Mini-maxers, despite the fact they often use game rules as character knowledge, can roleplay. What makes one a mini-maxer is not an inability to roleplay, but a tendency to wish to play only from a position of strength and advantage. Mini-maxers tend to use the rules as character knowledge as well.
Roleplayers, on the other hand, embrace a much wider variety of roles, from very weak to very powerful. Mini-maxers, though they can play their role of power well, do not tend to wish to play from any weakness, let alone many weaknesses. In fact, sadly, they may gripe, complain, whine, bicker, and sulk like any immature little boy might, should they not be allowed to have a powerful character and get their own way. *Sigh!*
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Emphasis is mine, unfortunately not in the original.