Not intelligence as in smarts (although that's important too), but intelligence as in information. Today, we are taught that success is a matter of willpower - of persistence, of grit, of continuing when failing.
Although failure is important to growth, the most critical factor in your success is the quality of your information. The more you know about the area you're trying to win in, the more aware you are of the opportunities - the strengths to avoid, the weaknesses to exploit, the options for mobility.
Want to land that new job? Research the company! Find out who their distributors and competitors are, their unique advantage, markets they are trying to break into.
Want to date that girl? Find out what her interests are. What does she like to do for fun? Which countries has she traveled to? What TV shows does she like?
Want to start a business? Find out as much as you can about your customers. What quality of product do they want? What inside jokes do they use? What's going to make them talk about your new product?
Want to invest in a company? Find out as much as you can from their financial statements, their management, their competitive advantage.
Intelligence marks the critical difference between playing to compete and playing to win. You can be confident, persistent, charming all you want, but those qualities just help you to compete.
To win, you need to know where, when, and how to make moves. That requires intelligence.