Theory #2: Cobb was in a dream all along since the beginning of the film
This theory implied that there was a level even shallower than the “airplane level”, and that level was reality. If this theory was true, it meant that Mal was right to convince Cobb to jump with her to return back to reality. But Cobb didn’t and remained in the dream while Mal went back to reality by dying in the dream.
When Cobb woke up in the airplane, it was a dream but he thought that it was reality. The whole end sequence had a dream-like quality to it with Cobb passing through the customs without a glitch, meeting Miles, and finding himself back at home with his children. He spun the top but walked away from it, confident that he was in reality. However, the top kept spinning and never came to a standstill, implying that Cobb was still in a dream. The split-second wobble of the top could be attributed to an uneven point on the table, a tiny depression of sorts that caused it to be momentarily unsteady.
Another observation was the sequence in Mombasa. Cobb was there to recruit Eames, but as he was chased by armed agents, he had to run into a gap between two walls that became narrower, causing him to struggle his way through. This could be a sign that it was a dream because it was unnatural in reality to have walls built unparallel to each other. Moreover, Saito, who was in his car, rescued Cobb in the nick of time. This could be read as merely coincidental but it would be very hard to believe unless it could be explained that “it was all just a dream”.
**The strongest argument against this theory was that if Cobb was in a dream since the beginning, who then sustained him in reality? Could it be Mal? Unlikely because if Mal jumped and returned back to reality, she would have tried all means to find Cobb and unplug him from the dream machine (because she was desperate for him to join her). If it wasn’t Mal, then who else? And for how long had Cobb been plugged into the dream machine if he was being sustained by someone? Was it even feasible?