The reason is that a certain algorithim will have a certain buy signal. To begin, the programmers will discover a very reliable buy signal, then write an algorithim to it, for instance, every time a currency moves up 0.5% in 3 hrs, to buy, or something like that. The robot will keep doing that, and profit, since people using other programs still believe that the currency wil keep going down, etc. However, if enough people use algorithim X, that buys at that signal, then not enough people will be selling at that same condition. Soon, this will cause the blanace of supply/demand to be thrown off kilter, and the new demand will change the actual price movement, and the algorithim will be rendered useless.

A lot of forex software are scams or plain useless; however, those which are profitable will not be profitable for long; once people realise their potential and enough people start using that robot, then it will be rendered useless once the forces of supply and demand shift because of the robot.
References :

BTW im not suggesting that a robot works, my suggestion is to learn how to trade forex, yourself.

it seems to me that with education and learning. probably some money laid out. that forex can be most profitable.
References :

I did used them before and I lost money with them until I was introduced to this site
Just go and check it out and see for your self
I used their software and in 18 days I made over $418 net profit
This wok…for real
References :
http://tradinglikeapro.blogspot.com
http://yourbizwebsitesreviews.com/FAPTurbo