Okay this sounds trite I know.. but
Every song I have truly "listened" to has had some effect on my life, just the same as any book I have read might have done so. Though because my musical tastes over the years have been so diverse it is hard to pick out the milestones. More often than not it has been a particular artist or group rather than a specific song that has caused me to stop in my tracks and review certain aspects of my life. I find it difficult in choosing my 10 tracks for my "desert island disks" (apologies to those outside the UK & have never heard of this), let alone pin pointing a particular song that has had such an impact as say "Late for the Sky" did for campfire.
That's not to say certain songs don't have a very special significance in my life (usualy to do with love), or that certain songs I have written are not special (again due to love). But if I was honest with myself there is one particular track that was responsible for my "introduction/appreciation" of blues music (I realise that for anyone who knows me via the mudcat, this is not in keeping with the usual Irish music I am perhaps more associated with). But through it, albeit over many years I got to sing in front of "ticket paying" audiences.
Ah.. those were the days.
I could go on forever about various artists.. i.e. Paul Simon because of whom I decided to learn the guitar, but I guess I've bored you enough as it is.
Mick