I agree with Xenth. The term "hardgainer" is likened to the terms, "not trying hard enough," and "excuses for not getting results." "Hardgainers" just want to blame their lack of results in something besides themselves.
Sure, there are different body types, and each has its own points that need more work. Learning and exploiting those points is what masses results.
Real life "hardgainer" example - Tommy Kono -
Tommy had severe asthma, people said he would always be weak and have health problems. He grew up during the depression. With little food and money.
Was transported to a Japanese relocation camp during WWII.
Was drafted into the Korean War in 1951. He basically had health and circumstantial situations that "should" have kept him from having results.
Yet, he still became one of the most successful Olympic weight lifters of all time, setting world records in 4 weight classes.
I have been lucky enough to have spent some time with the man and can say that he is one of the most giving people I have met when it comes to knowledge about training and life.
If one man can become great after all of that, YOU, can learn enough and work hard enough to get all of the results you can dream of. None of this is easy.
As long as there are people like him, and stories like his, (believe me there are 100's of them) I will go to my grave believing that a "hardgainer" is just not tough enough to get themselves results.
Stepping off soap box. - This is a sensitive subject for me since I was 5'11" and 100lbs at age 15. I benched 65lbs and squatted 95lbs. After having been weight lifting for 3 years.
I still was able to gain weight to over 300lbs. Squat 850 and bench 625, snatch over 350, clean and jerk over 425. Compete in Olympic weightlifting, Powerlifting, and Strongest man, over a competitive career of 12 years. EVERYONE, can get the results they want, if they want them bad enough.