[SPOILER ALERT]
 
Thinking back on Mal's jump to death scene, I can't help but think that Mal was right... about Cobb and her still dreaming. Cobb doesn't believe it.
&Nbsp;
"If we're in a dream, why can't I control this world [like when we built entire cities of our own]"
"BECAUSE YOU DON'T KNOW YOU'RE DREAMING!"
 
Mal keeps showing up as a projection or as a plagued memory in Cobb's reality. He either runs away, locks her up, or shuts her out. Because in dreams, Cobb can do this. When she jumped from that hotel room, Cobb lost the only real totem he had. Mal was the only real totem for him. Because she was there with him, as a real sovereign being, instead of being yet another projection he can manipulate (e.g. Mal's totem).
 
In dreams, you can create entire cities, but being aware, beholden of things like gravity and science takes a backseat. In reality, you can't build entire cities in a blink of an eye, but are more knowledgeable and tethered to lawful truths. Mal is probably in reality with those truths, knowledge, and technology that allows her to go in search for Cobb. Because of his disbelief he jumps from one dream to another, all dropping him further and further into limbo. It all started with Cobb tampering with Mal's totem. He knew Mal couldn't believe in her totem, and consequently, neither could he. Neither could he believe in her. Cobb tampered with the truth regarding Mal's totem, and lost Mal in the process. Now he's alone, deluded, forever alone in limbo.  
The point is that the story only makes sense if Mal was right. That they were still dreaming. And the only way Cobb will ever wake up from limbo is if he stops looking for random clues, and confronts the brutal truth of having to die to live.
 
What a poetic albeit cryptic plot line to tell the story of our lives. Of the tethered notions of truth, justice, and undying love.