They’re both sad, but for one road the person is dead and for the other the person is grieved/bereaved. Which is which depends on the interpretation of the song you prefer.
Let me start by warning you that the history behind this innocuous-sounding song is right in my wheelhouse, or up my alley, or whatever expression you want to use. I’ll try to rein myself in, but it’s going to be hard. So hang in there with me to find out more than you thought possible about a song you’ve probably heard many times but never questioned. Let me just quote the chorus before we get started:
O you take the high road, and I’ll take the low road,
And I’ll be in Scotland afore ye,
But me and me true love will never meet again,
On the bonnie, bonnie banks of Loch Lomond.
The person who takes the low road is going to get to Scotland first but won’t ever see his or her true love again. So who’s speaking, and what’s going on?