If you've done any amount of training, you will realize that some groups are easy to work with. Participants can be eager to learn from the training seminar, be active when you want them to be active, non-disruptive and helpful. But that's not always the case. Sometimes some or many participants in the group attending a seminar want to be somewhere else, don't want to participate in activities, are relatively inert, and so on.
Professional and expert trainers take the position that it is the trainer's responsibility to succeed, regardless of who is put in front of them in the classroom.
Less able and less responsibile trainers do something different. They attribute the failure of training (or difficulty) on the seminar participants. "Oh", the trainer says, "That was a bad group". Or, the trainer says "They simply didn't want to be there". Both of which can be true.
That said, having a group of people that is more difficult to work with is part of the life of being a trainer. Dumping off responsibility on them (particularly when the trainer gets paid to create results), is a cop out, and loses a valuable opportunity for the trainer to learn and develop. Think about a plumber. It would be a poor plumber indeed, who suggests that the reason the toilet is still leaking (after being paid to fix the thing) is because the "toilet" is tough, or unmotivated to change.
The point here is that trainers need to act as if it's possible to succeed with any group, and to strive to succeed with any group, and not to shrug, and excuse failure by blaming it on a poor group.
More on Trainer Responsibility: Making Excuses and Refusing Responsibility When Learning Does Not Occur During Training