The number one reason we dont make gains in size and strength is that we dont stick to a program long enough. Now some people have the ability to stick to a program for its duration. While others (like myself) jump to the newest program that one of the authors post.
When we jump from program to newer/better program, you are not giving yourself the time to adapt and progress in strength and size. We end up finding something that is more appealing to the eye. You may be doing a Waterbury program when all the sudden Thib or Staley puts info up, we jump over to it thinking it will give us better gains. What happens? Let down, we end up disappointed in the results cause we never gave it time to work.
I am trying to do better in sticking to a program. I started EDT two weeks ago and lovin' it. I hope to stick with it for a few more weeks/months. I hope this sheds some light on why some of us are not making gains.