when i started doing workout in gym i do take supplements but not gaining mass on my body..and also not increasing size..even i was training hard and lifting heavy sets..i was disappointed and take a break for about 6 months..then again i started workout but this time i also focus on the diet intake by me..and also i follow the mark manus advice from total anabolism of takin 3 sets per exercise of 8-12 i found that i'm gaining size and weight.so, according to me supplement only will not help u to gain size they just repair the muscles after workout and give u energy to lift more and workhard.The simple theory according to me is..
75% depends on ur workout plan + 15% depends on ur natural diet intake + 10% depends on supplement ur taking.
Anyone if disagree with me can post his view i'll b very happy to get corrected..!