When I was starting graduate school, at 23, there was a veteran PhD student there who was pretty sharp. Without realizing it, I started relying on him more and more, asking him where I could find this, what I should do here, etc. One day I popped into his office, and asked him where I could find something I needed, and how to use it. He stared at me for about 3 seconds, then said "***, can't you do ANYTHING for yourself?" I was ticked off! The guy WAS truly famous for being arrogant, and he held bad grudges, and had many weaknesses. I immediately focused on his weaknesses in my mind, and angrily set out to find the equipment myself. As I was working, I realized he was right, and was embarrassed, but also very, very thankful for his straight-forward criticism. Seeing my problem, and stopping my over-dependence got me through graduate school, and has helped me beyond.
You're right. I know you weren't talking about an enemy here, but... a wise man can take criticism, even from his worst enemy. After all, an enemy may give the MOST valuable criticism, because he's not prejudiced to like you.
Both of those morals you brought up are very applicable to the topic of this thread.