Opposition by-election victories are remarkably common.
Voters regularly use them as an opportunity to give the government of the day a well-deserved kicking.
And then, when the next general election rolls round, those seats often return to their original owner as constituents decide who they want to run the country.
Labour’s victory in last night’s Rutherglen and Hamilton West by-election feels different, however.
Firstly, the 20.4% swing from the SNP is truly extraordinary, and far above even the most optimistic Labour supporter’s expectations.
If - and it’s a very big if - that was replicated nationally, Labour would be on course to win more than 40 Scottish seats. At the 2019 election, they won one.
And that’s the second reason why last night’s result is a big deal. After the 2019 general election, Scottish Labour were on their knees. The SNP won 48 of the 59 seats available, confirming their hegemony north of the border.
Labour’s by-election victory shows that, less than four years on, the tide of public opinion is turning.
Thirdly, the Rutherglen result confirms that Keir Starmer is well on the way to becoming prime minister. Put simply, the more seats he wins in Scotland, the fewer he needs to bag in England to secure a majority.
As Labour activists prepare to gather in Liverpool this weekend for their annual conference, it’s the perfect boost.
The result also asks searching questions of the SNP, its relatively new leader Humza Yousaf and the party’s prospects of leading Scotland to independence.
Yousaf’s current strategy is to secure a majority of seats at the next general election and use that as a mandate to begin negotiations with Westminster. The evidence of last night suggests that is a forlorn hope.
Indeed, with the Scottish Tories hopeful of increasing their current tally of six Scottish MPs, there is a real chance that the nationalists are squeezed by both the Conservatives and Labour.
As one former Tory cabinet minister told HuffPost UK this morning: “The SNP could be wiped out in a pincer movement.”
Labour’s win in Rutherglen and Hamilton West may be just one result, but it’s implications for UK politics could be enormous.