Actually our greatest failure as a species is not thinking/planning far enough ahead.
Yeah, it seems we're more adept at letting problems happen (or repeat) and then struggling to solve them with significant stresses, rather than being proactive and averting problems before they have a chance to occur.
When you're solving problems in reactive mode, you don't have the luxury of taking your time and thinking things through thoroughly. While at times having the pressure of limited time can spark innovative and creative solutions that otherwise might not have been achieved without such pressure, I think it's safe to say that with less pressure and more time you have the opportunity to further scrutinize the gamut of possible solutions and choose the best.
What I had posted earlier was more of the "best case scenario". But I do believe it'll likely be more as Crazy Eddie depicted it. We will expand beyond the Earth, but only because we're forced to by other circumstances. Knowing how humanity operates, we're bound to screw things up here on Earth and make life barely tolerable for a good many people. But from a practical standpoint, I think colonizing the ocean is a far more feasible endeavor than trying to colonize the moon or Terra-form Mars.