I think that when Superman manages to beat the odds to win impossible odds, it sends a stronger message then simply accepting defeat: it encourages people to think "nothing's impossible, so long as you perservere."
However there were things that even Superman could not do. He wound up in Krypton past numberous times and failed each time to change anything.
The efforts to explain his inaction during WWII didn't come together until the
Spear of Destiny and Holy Grail ideas came along. He and luthor teamed up to end world hunger - another disaster. His efforts at finding an antidote to Kryptonite were a total bust even thought Luthor supposedly made the original antidote from a lab Superman himself had built.
Yes there were time when Superman could beat the odds but there were oter time whent he odd should have been in his favor and he totally botched the job.