The reason- you have to know the player and his tendencies.
Of course it "depends", however, what the novice is usually asking is if there is a reasonable "default" play against an unknown opponent for the given situation. After all, if they knew the player well enough to know his tendencies, they probably would not have needed to ask the question in the first place.
Like it or not, in poker there is almost always a default play. Take the following scenario for instance:
$1/2 No Limit Hold'em
Everyone folds to you on the button, and you raise to $7 with KhQh. Only the BB calls and the flop is JhTd3c. The villain bets out $4 into the $15 pot.
What you know about the opponent is fairly irrelevant here, because you ALWAYS should raise. His bet is pretty much universally weak, and your hand is always live, so putting him all in will usually make him fold, but you don't really care because his stack size guarantees that you can never make a critical mistake.
Furthermore, the smaller the stack sizes, the more the poker math supersedes the art. In fact, given a small enough stack, certain plays become always correct or always incorrect, such as this...
$1/2 No Limit Hold'em
You are dealt KK UTG in a 6 or more handed ring game.
Your opponents tendencies mean nothing as you are probably best at this point. Folding is obviously out of the question, but if you limp, you are now giving the small blind automatic odds to call you with a single ace in his hand. Ditto if you raise the minimum, only now the BB can make the same call. Therefore you always go all in.
This argument I am making is for far more than academic discourse. Knowing default plays and tendencies of strangers is of paramount importance to successful multi-tablers. You are constantly faced with a new line up and many of your opponents will go broke quickly and will never be seen from again. And if you are playing 6 tables or more, you will rarely get specific reads on these players and must make the mathematically correct play that is relevant to the given situation.
A simple run-down of these plays is listed below:
- Raise and re-raise big pairs
- Bet and raise strong hands on the flop
- Don't make big folds with top pair/good kicker or better on safe boards
- Don't make big calls on overbets on sequential boards or 4 flush boards
- Pay attention to the odds
- Don't respect small and min-bets
NEVER, EVER, EVER fold Kings before the flop!!!