If there's one word of advice Pixar animator Austin Madison would give aspiring creative people, it would be: "persist". Actually, in all caps. He too, goes through the struggling, frustrated "quagmires of discouragement and dispair" 97 per cent of the time.
To get to the 3 per cent that you will be remembered for, you need to persist. Here's the full note of inspiration (click to expand) or you can read the transcript at Letters of Note:
Peter Jackson's quote, "Pain is temporary. Film is forever." (and the similar "Pain is temporary, quitting is forever" quote attributed to Lance Armstrong) may also help you persevere.