Probably both. Some people don't like to see others succeed as it they think it makes them look diminished. Some people are incapable of doing certain things (due to mental, physical, or academic reasons). So if they cant do it no one else should either. Therefore, they criticise and discourage other people from doing that thing.
Some people have massive egos and think they are greater than everyone else (conceited). These people are so insecure that they "lord" themselves over others over other people and discourage then from trying to succeed lest they be seen for what they really are - nothing.
Thank you for your thoughtful and helpful reply Shuhak. Love your tag line. I'm a good cheerleader and I bet you are too. Some folks would rather drop dead that say an encouraging word to anyone. I'm gonna ask why that is! :)
Shuhak 