To repeat-
“To offer a man unsolicited advice is to presume that he doesn’t know what to do or that he can’t do it on his own.”
- John Gray

The above one sentence says it all. The main problem is when you give unsolicited advice to another person, you are implying you know better than they do, and that they are are doing something wrong.

I just had an encounter with a new tenant in my old flat who gave me unsolicited, and quite wrong advice. It is such a big turn-off to receive ignorant, misinformed advice from a person who does not even understand the situation, e.g. my business. Perhaps the quickest way to lose a potential business connection is to tell another person who to manage their affairs!

My final comment on this thread: the times we live in today are times where everybody seems to be talking–and nobody is listening. It makes sense there is more unwanted “advice” being offered. Don’t do it. You’ll get much farther keeping quiet and, like the author above says, if you must give advice be extremely careful about if the context is right, and the person will even listen. To be wrong in this is to risk losing the association altogether.