The first time a person gets honest feedback on their work is hard because they are often surprised.
"Visual literacy" is as hard as learning to read well. But unless a person has studied art, they haven't had much chance to develop the skill of "seeing" well and this makes for a lot of surprise.
One challenge is that people offering advice may also not be as skilled at seeing well, either, so the advice isn't always useful.
Another challenge is that people have learned "rules," like the rule of thirds, and they apply the rule to every image. Try that with great paintings or great photographs and you will see that they don't slavishly follow the advice. But some critics do because it is an easy thing to learn and apply. 
Finally, there are people who feel under appreciated and try to feel better about themselves by striking out at others (the "jerks"). These folks muddy the waters a lot.
So the trick is to keep the feedback productive. If you consider how you would feel on the receiving end of the way you express yourself, you are far less likely to be a jerk. And if people react defensively to your comment, see it as an opportunity to think about how you are saying things and examine if you could have said it better.
That doesn't mean the criticism might not be valid, just that if you are delivering critiques you should also be open to having your words critiqued, too.
It is easy to blame the other person. 