Enthusiasm - A state of mind that inspires and arouses one to put action into the task at hand.
By mixing enthusiasm with your work, you will never be bored and the work will not seem hard. The old saying "If you love your job, you will never work a day in your life", comes to mind. Enthusiasm about a task also enables you to perform more work in a given time without becoming tired.
Even if you are currently in a job that you do not enjoy, due to other circumstances, you can still continue to plan and work on ways to achieve your definite purpose that you have set for yourself in life. As you develop enthusiasm about your definite purpose (your long range goal), no matter if you are in position to achieve it at this time, you are still setting the stage for that end result.
Enthusiasm is the sparkle in your eyes, the swing in your gait, the grip of your hand, the irresistible surge of will, and energy to execute your ideas. - Henry Ford
SO the action of enthusiasm must be followed with words of enthusiasm in order for it to be able to apply the principle of suggestion. The other part of suggestion has to do with your thoughts, as most things usually do in this book and in many others out there, including The Secret. If your thoughts, your words and your actions are in harmony, you are bound to influence those around you.
Now you may say that you are not in the selling business and that is not part of your definite purpose, but I say that we are all in the selling business when it comes to our definite purpose. You may have to "sell" a significant other on the idea you are presenting, maybe you have to "sell" your current employer on an idea that will get you to where you see yourself in the company, etc. In order to get to your definite purpose you sometimes even have to "sell" yourself on the idea that it is even possible. Being enthusiastic about it is one of the principles that will get you there!
Now I must warn you that as it is with all thoughts, actions and words. Negative ones will come to pass just as readily as positive ones. So doing, saying or thinking things that are negative in an enthusiastic way will bring about the same result!
Every production of genius must be the production of enthusiasm. Disraeli