All of these are possible reasons why someone would not want to take your advice.
Perhaps the most dangerous reason, however, is that most people think they already know what you have to say.
When it comes to building muscle, there are a lot of different factors that play in to this.
You have to lift weights with a certain intensity and volume, and you have to increase your calories accordingly.
You have to include healthy foods such as fruits and vegetables that may not normally be considered when trying to build muscle.
There are also many other considerations in a training program which are beyond the scope of this article.
One point here is that many strength trainers and bodybuilders think that they already know these things.
The obvious danger here is that such people will stop learning, and this will eventually limit their results in the gym.
More than this, though, is a danger that people think they know something but never take action on it.
Yes, there is a danger that people think they know everything about building muscle when they really don't know very much.
But let's assume that they do know a lot, at least they know some theories and jargon.
There's a big difference between knowing something and taking action.
If you want to achieve great results, find yourself a great mentor or muscle building program.
Learn from it and follow the instructions closely, because action is the only thing that will bring you success.
Anyway, until you take action, you can never truly know something.
You just have to trust me on that.