THERE was a great little Facebook video the other day that I watched on the bus on the way to work, about how tribalism works.

It explained, in a helpful animation with subtitles that made me feel like a well-informed moron, that in order to counter tribalism and have any hope of ever changing someone's mind, it's vital to first establish common ground with an opponent and break down tribalism's protective barriers. If you don't, and just keep barking your opinion at someone, it tends to have a backfire effect, in which their existing position will become even more entrenched despite your attempts to dazzle them out of it with facts and logic.

I thought of it again last week after a stramash on Scottish political social media when Cat Boyd, a prominent figure in the indy movement and the Radical Independence Campaign during the referendum period, said on a television programme that she'd voted for Labour in the General Election.

The reaction on social media was way over the top, to say the least. Cries of "traitor" and "betrayal" dragged on for days, and some were genuinely bemused that a committed Yesser had voted for a unionist party.

I began to wonder whether I was the only person who didn’t see Boyd’s choice as a threat, but as an opportunity.

Unlike social media’s tribalists, Boyd has far greater opportunity to gain numbers for the independence movement. Indy-or-nothing is not her starting point; independence is simply one point on what she sees as a bigger journey towards a better way of living. That desire is the common ground that the independence movement tapped into in 2014. Indy became a route rather than an end goal.

It's no surprise, then, that people like Boyd look to someone like Jeremy Corbyn and become attracted to that same energy, even if ultimately a Corbyn government would be constrained by the same establishment structures the indy movement is so close to tearing down.

It's also worth remembering that this was a Westminster election, and we've had a sufficient enough time of devolution for many younger Scots in particular to see a very functional difference between our two parliaments. The mandate for a second referendum comes from Holyrood, not Westminster, and people like Boyd who voted for Corbyn are still committed to independence.

The apparent impossible contradiction between being a passionate Yes campaigner and voting for a unionist party is not all that impossible. It reflects a dominant feature of the indy campaign: it wasn’t about nationalism for nationalism's sake, it had to offer more than that.

And that's where Boyd and others like her have the upper hand on the common ground. Her motivations are clear and consistent when put under the spotlight, and that gives her pro-indy analysis far more credibility with potential Yes voters than those who exude a more nationalist mindset, simply becomes it becomes hard to believe she would sacrifice the bigger picture for the sake of winning one vote.

Meanwhile, there's a very real worry brewing for the independence movement and it’s not the number of Yessers who voted Labour in 2017, it’s the number of SNP voters from 2015 who didn’t turn out at all. According to YouGov, that figure is at an alarming 23 per cent.

If, say, Momentum began a campaign in Scotland, sensing that there may be the possibility of a much bigger comeback here should there be another General Election, it could be a real asset for Yes that the likes of Boyd have built up trust and credibility among wider sections of the voting public. Her Labour vote this year was a signal that her politics transcends any nationalist-unionist tribalism, which could prove vital in stemming the kind of Labour comeback that could become a problem for the Yes campaign.

Someone like Boyd can make representations for the indy movement among like-minded people and bring them over to Yes, rather than entrenching them further into unionism with tribalist polemic.

It may be hard to many Yessers, who feel betrayed by a Labour party that joined ranks with the Tories in 2014 to oppose them, to stomach the thought of voting Labour. But nobody saw Jeremy Corbyn on the horizon after the referendum, and to deny that he's changed the dynamic is to deny reality.

The independence movement must think more tactically about revelations such as Boyd's. Winning independence will require winning previous unionist voters over, and that isn't going to happen by digging trenches.