TTC First Time Chance/Likelihood

I've searched around the forums a bit and haven't really gotten a good indicator, so I thought I'd ask. What's the likelihood of conception during your first try? I've searched a bit online and it mentioned 80 something percent get pregnant by their third month trying. However, I hear about a lot of people having difficulty around this forum. Is that just because this is where people flock when they are having difficulty or are the chances of conception that slim?

Just curious on everyone's success rates.

Thanks in advance.