>>988818
That and his psychological need to always shoot himself in the foot. He's like Evan Dorkin, who had a severe nervous breakdown, and hasn't been the same since, because he just realised he'd gone from fan to pro.
Thanos always accumulates power, and displays brilliance is doing so, then stagnates when he has supreme power, leaving himself open to simple attacks until one works.
He always chokes on the cusp of success.