So. Lots of sites use draws as an example. I have a straight draw, my opponent has a flush draw.
He bets and now I gotta decide to call.
So, lets say you're on the turn. You both have those draws. Preflop, he was mid position, so were you. You're in there with suited connectors which is why you got a straight draw. Your opponent, for the sake of simplifying the math, will have any 2 suited cards 50% of the time. And he calls any flop bets. No matter what. So you're at the turn, and he bet so now you now there's a 1 in 8 chance that he's on a flush draw. At the turn, he'll hit his flush around 1 in 5 times. You, with your 8 out straight draw will hit your straight 1 in 5.75 times. In the 1 in 23 chance scenario that you complete the straight draw and he completes his flush, you gotta ask yourself, will you lose more than you make in the other 22 scenerios where you hit a straight and he misses his flush or both of you miss?
Also, in addition to that, remember to keep the implied odds in mind cuz you shouldn't even considering calling that bet if you can't multiply the amount you're putting into the pot to call by 5.75.
Good luck. I believe the numbers are close to accurate.