People have varying accuracies of "gut-feel". But the only way to get scientific about betting is to do the math. That means diligently counting outs, and calculating and comparing card odds and pot odds. Card odds indicate your chances of receiving an out card that makes your hand a winner. Pot odds indicate the value of the pot relative to how much you must bet to win it. When card odds are equal to or better than pot odds, it's reasonable to stay. Otherwise, it's more reasonable to fold. Scientific players will beat pure gut-feel players in the long run. Poker Odds for Dummies and Poker Strategy are great guides to poker odds and Texas Hold'em strategy. Also, when playing online you can leverage certain tools and odds calculators so you don't always have do the math manually.