Here it is. The characteristic that, above all others, marks out those who have acheived great things; in business, in sport, in politics, in the field of science.
Belief.
Sure, you need other things; you will not be good at anything without determination and perseverence, but those will come from your belief. If you want to do something with all your heart and you believe that you can do it, then you will succeed.
"Whether you believe you can do a thing or not, you are right." Henry Ford
Belief is deeply engrained in our subconscious. You can tell yourself you believe you can do something but not really feel it inside. This is common in many entrepreneurs who have run businesses that have become 'stale'. They set off on a business adventure to greatness and have managed only mediocrity.
In cases like this experts often find that the once-upbeat entrepreneur still manages to show some enthusiasm but behind closed doors has lost the belief that they can do something about it. The trick is to come out of your business - mentally and physically. See it as though it was somebody else's and imagine telling them what you would do to make it better. Many of the marketing ideas on this site will help you. It can be quite amazing how a change of perspective works.
Once you have seen that it can be done, implement the best ideas and see the results. The proof then deeply re-ignites the belief.