Conall McDevitt's resignation wasn't just a personal political debacle. His loss will be a body blow to a party which was just recovering its equilibrium.
He resigned after admitting undeclared payments from Weber Shandwick, the PR firm for which he had previously worked, even after becoming an MLA.
He might have got away with a letter of apology to the Speaker and his party leader but for other questions about payments which he had made from his Assembly and Policing Board allowances to JM Consulting, run by his wife Joanne Murphy.
As a PR professional, he will have known that, at a certain point, even a single grain of sand added to the scales tilts them against you.
He will also know that he was getting little sympathy because of the standards he had demanded of others in public life.
Nelson McCausland, the Social Development Minister, and Matt Baggott, the PSNI Chief Constable, are just two of the people he had lectured on their responsibilities in recent months.
That rankled, but within the party, great things were expected of him.
In 2011 when Dr Alasdair McDonnell, aged 62, was elected leader it was predicted that, after a period imposing order and discipline, the veteran MP would be succeeded by Mr McDevitt, who was 39 at the time.
Although there would be other claimants, that still seemed likely until yesterday.
He was popular with voters and lobby groups and was the poster boy for a version of the future which intrigued many people, both within and without the SDLP.
A Dubliner descended from a Belfast republican family, he epitomised a broad Irish national vision without being a traditional nationalist. He liked to describe himself as "a southerner by birth, a northerner by choice".
He talked of leading the SDLP into a voluntary coalition as the next stage after becoming leader.
He began his political career in the Irish Labour Party and that gave him a social democratic, non-sectarian vision of the future.
"The principle duty of the SDLP is to make the North work," he told me in an interview.
"Our priority is to make this region a success whether it is a region within the UK, which is the current situation, or whether it becomes a region within a united Ireland."
He talked about a new Ireland emerging gradually over 50 or 100 years, but not within his political lifetime.
The political debate will be different without his contribution.