Unsolicited Advice

I'm just pondering this morning why we, as humans, give unsolicited advice. It's one thing to ask someone for advice, but why do we offer it so often when it isn't requested and, quite frankly, not needed.
I was recently asked for what I interpreted as advice. I then proceeded to give ALL my feedback and didn't restrain. I should have clarified some points before just dumping all of my assumed expertise in the area...and that assumption was on my own part, not on the poor soul who asked a simple question. I didn't think anything of it at the time, but am now pondering my response because several people have now vomited their advice about my life unsolicited. I say "vomit" because it happens all the sudden without notice and it's all out before it's done...no one can seem to bottle it up.
Because this can seem quite the contradiction, I am first putting this out here for anyone who has ideas on why we do this but also how to check yourself so that I can NOT do this again. And, thirdly, I would love to hear your thoughts on how to kindly and gently but assertively guide a conversation away from the advice column.