I love this short article on unsolicited advice. The quote I particularly agree with is:
"3 — The giver of unsolicited advice often makes the erroneous assumption that the receiver has goofed because of lack of knowledge.
What the giver does not realize is that the receiver either (a) does not agree with the giver’s opinion or (b) has made the error because of lack of time — or because fixing it is not a priority."
I've noticed a very common tendency among humans to dole out unsolicited advice. This behavior amuses me whenever I see it...simply for the reasons outlined in the above blog article.