Well it's a bloody long story with not one specific thing.
Like Jim Lad our family always sang. Even though Dad couldn't carry a tune in a bucket it didn't stop him. Mum would play the piano whenever we went to a pub.
Then there was this music teacher at school, can't remember what his name was, but he just gave up on trying to teach music to a bunch of rowdy boys, and he'd sit at the piano and we'd go through the song book. Most of which was folk songs 'cos they were out of copyright.
I didn't find out until later that most of them had been Bowdlerised.
It took a few Rugby songs for me to discover that. It's surprising what you can learn as second rank scrum!!!
Then there was Lonnie Donnegan which sparked further interest which led to other discoveries such as Bernard Miles and Bernard Cribbins and Paddy Roberts.
Then when I was on a contract in Bahrain, after reading just about every paperback of junk fiction, I happened across a book of folk music by Tom Glazer which had a chapter in the back on guitar playing.
Having a few Dinars to spare at the time I went and bought a guitar.
Three chords later, here I am.