Min/Maxing (DMG)

Sometimes players resort to "min/maxing" when selecting weapon proficiencies. Min/maxing occurs when a player calculates all the odds and numerical advantages and disadvantages of a particular weapon. The player's decision isn't based on his imagination, the campaign, role-playing, or character development. It is based on game mechanics—what will give the player the biggest modifier and cause the most damage in any situation.
A certain amount of min/maxing is unavoidable, and even good (it shows that the player is interested in the game), but an excessive min/maxer is missing the point. Reducing a character to a list of combat modifiers and dice rolls is not role-playing.
Fortunately, this type of player is easy to deal with. Just create a situation in which his carefully chosen weapon, the one intended to give him an edge over everyone else, is either useless or puts him at a disadvantage. He will suddenly discover the drawback of min/maxing. It is impossible to create a combination of factors that is superior in every situation, because situations can vary so much.
Finally, a character's lack of proficiency can be used to create dramatic tension, a vital part of the game. In the encounter with kobolds described earlier, the player howled in surprise because the situation suddenly got a lot more dangerous than he expected it to. The penalty for nonproficiency increases the risk to the player character, and that increases the scene's tension.
When a nonproficiency penalty is used to create tension, be sure the odds aren't stacked against the character too much. Dramatic tension exists only while the player thinks his character has a chance to escape, even if it's only a slim chance. If a player decides the situation is hopeless, he will give up. His reaction will switch from excitement to despair.