Is the glass half empty or half full? I know it's an old cliche, and it's been duplicated on thousands, if not millions, of blogs regarding the same subject I'm about to talk about, but it just works so well.
Our lives are filled with struggles. Even the most successful people have troubles here and there (if not more than the less successful). The point isn't really about career success, though. It's about quality of life.
Being content with what you have is going to give you the clarity and type of energy that will help you make the assertions necessary to be successful. How many successful businesses are developed with the entire staff thinking how badly they are going to fail? In fact, why would you even go through with an idea if you thought it was destined to fail?
The thing is, when you actually try something, you have already increased your odds of attaining your goal (whereas the odds before you tried it were 0). And experience is always the valuable by product of any endeavor. Trial and error over time will hone your skills and show you what works.
After all: You gotta fight, for your right, to paaaaaaartay