Originally posted by super pr*xyCorrect. Cobb and Mal reached limbo by accident. So how did he know that only one more dream-level (a 4th layer) was required to reach limbo the second time? Better yet, considering Ariadne had no prior knowledge of limbo, how in the hell was she able to postulate that little factoid? (it was HER idea to retrieve Fischer from limbo in the first place)..? Overlooked plot-point, perhaps?
with cobb and mal, they were experimenting and got lost because they tumbled into limbo and couldn't wake up.. they reached that plane by accident..
And did anyone else get the feeling that the 'inescapable' quality of limbo had been grossly exaggerated? I think Cobb bent the truth about limbo because he didn't trust himself there. He knew Mal would constantly tempt him to stay, and/or harm anyone he was with -- so he made it out to be this hellish place that would ultimately consume you... But think about it: all he and Mal had to do was commit suicide via train to exit limbo the first time (just like ANY other dream-level).
The ease in which Cobb knew he could leave limbo is likely why he didn't hesitate to stay there to rescue Saito. He knew that once Mal had been dealt with, and once he had found Saito, they were only two bullets away from waking up. It seems that as long as you know you are in a dream, or you are with someone who can remind you of that fact, limbo is really no different than any other dream-level. In fact, it would probably be the best place in which to hone your manipulative skills (as you would have a completely uninhibited 'pallet' to work with.)
Cobb was just being selfish with it. sly