Who are my competitors?

I as a business student had always been taught in the subject of marketing that in order to survive in the business we should fight against our competitors. We should predict there future strategy and act according to it. We should create a PoD (point of differentiation) to keep away the competitors for the longer time.
But, when I gave this a thought I came across to a very different thing. In order to fight with our competitors we must know who our competitors are. Then I asked myself a question can we find our competitors easily? The answer to this question I got is no. The first thought came to my mind was for the product ‘Video Conferencing’. I attend one insightful session through VC (Video Conferencing) and started thinking with whom it is competing and which are the industries which are getting affected by it. I surprisingly found that the highly effected industry was the Aviation industry. Organizations have started using the facility of the video conferencing through which they are cutting the cost of travelling of their higher level executives.
The next industry which I thought about was of music industry. It was very strange to know that the Airtel is enjoying the highest revenue in the field of music through its caller tunes facility. If we look at the sale of camera, Nokia in India sells the highest numbers of camera through its cell phones than the major players like Canon or Nikon. The organization manufacturing alarm watches became the sick units just with feature of Alarm given in the cell phone. The launch of the iPhone and other mp4 players had just removed the Walkman players of Sony and other major players. The rise on online social media has completely changed the scenario of the gaming industry. Social networking web-sites like hi5 has far more users than the one who purchase games from the physical form of market.
So, did anyone know that Airtel would be having the highest revenue in the field of music? Was Canon ready to fight with the inbuilt camera in the cell phones? Was the Alarm clock industry aware of the alarm feature in the cell phones? Was Sony able to predict that the company like Apple would come with the product like iPhone and change the whole scenario of music industry? Was the gaming industry were able to predict the threat of the rise of the online social networking?
If we give a rational thought to the above question the obvious answer would be no or it might be difficult to identify our competitors. So to survive in this continuously growing market we need to update ourselves every minute. Being a king of industry and ruling the market for the longer time is no more possible. Our competitors are everywhere and to sustain we need to take it as a challenge and come with more innovations.