Why/how Is this song in my head?

[Dontbescaredlittlebear]

So I’m on my way home, a couple of sheets to the wind - where the fuck does that saying come from? - and I find myself humming ‘it’s my delight on a shining night, ‘tis the season if the year’.
Where has it come from? I’ve googled and it’s a real folk song, but I don’t ever remember learning it at school. Why is it in my head?

It’s been on an ad. I’ll try and find it.

Can’t find it on a quick google but the reasons I get in my head are as follows:

A recent ad
Grade 1 piano two years ago
It’s very similar to ‘a finger of fudge’

Thanks enb It is similar to a finger of fudge, but the lyrics were part of the hum and are obvs different . I have never done a piano exam!