Why are the chances to concieve only 25%?

Ok, so I know that 25% is technically high - I mean 1/4 of people who try to get pregnant do - but I'm curious why it isn't higher?

Does it include everyone, or just people who are really trying?

I realize that if it includes everyone: those who drink, smoke, are significantly overweight, are significantly underweight, don't pay attention to their bodies (BBT, OT, CM, etc.) then this would make sense...but for those who are so careful and aware and healthy...is it still only 1 in 4...and if so why?? That just doesnt make sense...

Can't find the answer...

I think that I'm not officially going to have much of a chance until my husband's little guys recover from Ironman - and that isn't going to be until the middle of January (75 days since Ironman) - so, we can practice, but it will probably be a while...