Christians - why do some people believe that those who go to hell will burn forever?

And then others (all professing to be Christian) don't believe in hell at all, but rather that it is metaphorical, and not a place? I believe there is a hell that God created to cast Satan into, along with his demons, and that those who follow Satan's ways rather than God's will follow them there, even though it wasn't meant for them. I DO NOT however, believe that people would burn forever there. After all, doesn't John 3:16 say that those who believe will not PERISH but have everlasting life? If you're burning in hell forever, do you not still have everlasting life, albeit not a very happy one? I can't see how it's logical to believe that somebody would burn there forever. Maybe the flames are eternal, but nobody would burn in them eternally, as I see it. So I'm just curious what the general consensus is among Christians out there. If you don't consider yourself to be a Chirstian, please answer a question directed at you - I'm interested in the various views on this subject from other Christians.