CNN —  

The conventional wisdom – even as senators flailed and failed to find a deal to keep the government open late Friday night and Saturday – was that this would all be over soon.

The disagreements were real between the two parties, but the desire to look competent in the eyes of the public would bring warring lawmakers to the table. If the Senate only had a few more hours after the midnight Friday shutdown, they would have made a deal!

And, they still might! After all, the relative pain – politically and in real-world terms – of a government shutdown doesn’t truly kick in until Monday when everyone goes back to work. Which makes Sunday a critical day for all sides involved in the shutdown. (The next scheduled vote in the Senate on the current four-week continuing resolution is Monday at 1 a.m. ET.)

But despite all of the assertions that a deal is in the offing, there isn’t a deal yet. And the three-week continuing resolution that Sen. Lindsey Graham proposed late Friday night, which was seen by Republicans as the vehicle to end the shutdown, appears – at least as of this writing – to be dead in the water.

The case can be made, in fact, that if no deal gets done within the next 36-ish hours, this shutdown may go on longer than anyone in Washington expects.

Here’s why – and it’s mostly human nature.

Think about the time in your teen years when you went with your friends out to the abandoned quarry that had been filled in with water. (Ok, maybe just me – but stick with me!) It was against the law to jump off the cliffs and into the water. You could hit a piece of the old equipment they dumped down into the hole and die – or so my mom told me.

The first time you jumped, you did it only after negotiating with yourself for a while – trying to calculate your actual chances of getting arrested or dying versus the shame you would incur among your friends if you didn’t jump.

But once you jumped that first time, it got much easier the next time. And easier the time after that.

My point is this: There was a huge push to keep the government open all the way up until midnight Friday. The images from the Senate on Friday night were remarkable – senators huddled cheek-to-jowl in hopes of getting something done. But once they all jumped into a shutdown, the urgency on Saturday seemed to leach away with every passing hour.

And by 7 p.m. Saturday it was clear that nothing was happening. The Senate adjourned just after 7:30 p.m. ET. A source close to the process told CNN’s Jim Acosta that the proposed three-week continuing resolution was dead in the water and that there was no next plan waiting in the wings.

Illinois Democratic Rep. Raja Krishnamoorthi acknowledged to CNN’s Tal Kopan that concern is growing that the shutdown could go longer than initially expected.

“I think there is that anxiety,” he told Kopan, adding, “with each passing day I think they grow more concerned that folks who are hurt by this shutdown are going to say a ‘pox on everyone’s houses’ and so we all have to make the government work.”

Concerns about being blamed by voters could well be the push that both sides need to end the stalemate. The longer a shutdown goes on, the bigger the stakes. All politicians are motivated by their own instincts toward self-preservation. If either the Republican or Democratic rank-and-file panics, it becomes very hard for the leadership to continue to hold out for their wish lists to end the shutdown.

All of which is to say that, yes, the most likely scenario remains a relatively brief government shutdown. But remember that the 2013 shutdown lasted more than two weeks. And there’s at least a chance that this shutdown follows that same blueprint.