Having a competitive nature is not a bad thing.
To flourish in any field, one must have the desire to be the best at what they do. Having the knowledge of what your competitors are doing with excellent results and adapting it to your marketing methods is a smart way to increase profitability.
Many successful affiliates also take part in competitions for monetary and physical prizes. This is an excellent example of how having a competitive nature can assist you in your affiliate marketing endeavors.