Everyone has influences. Ingres adored David. If he had talked himself out of painting because "it had all been done before" the world would be a much uglier place to live. The fact is that while your style may reflect the influence of Avedon or Adams, your photographs can only be made by one person: you. No one else has your same set of beliefs and experiences; replication is impossible.
I think you have to keep moving forward every day, and recognized that it's no easier to make a great photograph than it is to make a hole in one on a 200 yard Par 3. In fact, it's probably much more difficult.