The bombing is a sickening reminder of past atrocities and possible future traumas
The bombing of a civilian bus in the northern Lebanese city of Tripoli could hardly have come at a more sensitive time.
It was less than 24 hours after a parliamentary vote of confidence in the new unity cabinet, which hopes to end months of sectarian infighting.
And it was just hours before the recently-installed president, Michel Suleiman, went to Syria hoping to start a healing process after decades of aggravation between the two unevenly-matched Arab neighbours.
The bombing, which killed at least 14 people, also hit an area that has rapidly become Lebanon's most volatile security hotspot.
Tripoli has a large Sunni Muslim majority who, culturally at least, seem very Syrian - given the city's proximity to Syria's coastal cities.
But in fact they are mostly staunch supporters of Lebanon's pro-Western, anti-Syrian bloc.
There is also a small enclave of Alawites in Tripoli's poverty-ridden northern suburbs.
Their sect is an offshoot of Shia Islam based mainly in Syria - its president, Bashar al-Assad, is a member - and they are allied to the powerful pro-Syrian political and militant movement, Hezbollah.
In more politically stable times, this divide might not have produced serious problems.
But in the past months bitter street fighting has erupted between Tripoli's pro-Syrian Alawite enclave, Jabal Mohsen, and its neighbour, the mainly Sunni, pro-Syrian Bab Tibbaneh, leaving more than 20 dead.
Another Tripoli problem in the last 12 months has been the emergence of Sunni Muslim extremists, who are anti-everyone except al-Qaeda, in the Nahr al-Bared Palestinian refugee camp, just north of Tripoli.
It took months for the Lebanese army to quell the so-called Fatah al-Islam uprising last year. The camp was bombed to smithereens and hundreds were killed, and it is far from clear that the extremists were mopped up entirely.
Wednesday's bombing comes at a time when Lebanon could be about to turn a corner and leave behind the last four traumatic years.
The trouble started in 2004 with rumblings against Syria's continued domination long after the 1975-90 civil war, which Syrian troops helped bring to an end.
A Qatari-mediated accord fuelled some optimism Lebanon's strife could be brought to an end
And it literally exploded onto the world's consciousness with the assassination of the former PM, and anti-Syrian figurehead, Rafik Hariri in 2005.
Since then Lebanon has seen a string of political assassinations, a devastating war between Hezbollah and Israel, militia battles, and a lengthy wrangle over appointing a president.
But for the most part there has been a merciful absence of the kind of indiscriminate terrorist atrocity seen in Tripoli on Wednesday.
Then, in May 2008, a Qatari-mediated accord fuelled some optimism that the strife could be brought to an end.
Former army chief Mr Suleiman appeared a reassuringly unifying figure. The unity deal allowed government to be shared between a pro-Western majority and a veto-empowered Hezbollah-led minority.
The rival camps seemed to have set their disputes aside for later, over issues such as Hezbollah's sizeable arsenal and redistribution of electoral constituencies.
Unfortunately it tends to be at transitional times like this that the dark figures behind the violence in Lebanon strike.
Apportioning blame for a bombing can be a quick process in Lebanon - usually informed by political allegiances rather than hard facts as the perpetrators seem never to be caught.
This attack is different however, as it did not target a political figure, but rather a city where many fear the on-going violence could drag Lebanon back to the turmoil seen before the May accord.
The bus had just arrived in Tripoli from the northern Akkar region. Most of the victims seem to have been off-duty soldiers coming from an area known for its strong military traditions.
Suspicions therefore could focus on Fatah al-Islam, or another shadowy Sunni extremist group, perhaps wanting vengeance for the battle of Nahr al-Bared or hoping to sow seeds of conflict between Shias and mainstream Sunnis.
The timing could also suggest a link to Lebanon's political internal divisions, perhaps a group with an interest in prolonging the instability or warding off a rapprochement with Syria.