Problem w/ pot odss

[James Boston]

Here's a question about pot odds. Perhaps I'm just thinking about this wrong. (* for the sake of making this simple I will use a flush draw for all examples) I know (based on reading) that with four cards to a flush after the flop you are 2-1 against making it with two cards to come. But, you are 4-1 against making it on the next card. Shouldn't this be how your decision is made? If 2-1 gives you acceptable pot odds, but you don't get the card, you can't continue using the 2-1 odds for the next round of betting. It seems to me that if 4-1 gives you correct pot odds, you should bet. If you make your flush, play it accordingly. If you don't make your flush. Re-calculate the pot odds after the turn and determine if staying in the hand is still justifiable. Is my thinking on this wrong?