But the tens of thousands massing daily in Cairo's Tahrir Square remain fired with enthusiasm - at times a euphoric fervor seems their only fuel - and vow they will not back down in their demands for President Hosni Mubarak to step down and end his nearly 30-year rule.
How long they can hold out has become a crucial question in the crisis gripping Egypt, as the government appears to be digging in, reckoning that it can ride out the wave of unrest.
That means the confrontation could be turning into a test of sheer endurance. Protest organizers believe they must keep up the pressure of large protests, paralyzing the downtown heart of Cairo, to force the government to make a true move to democracy and not just cosmetic changes that allow the deeply entrenched regime to preserve its grip on power even if Mubarak eventually goes.
"We have to be steady to topple the government," said Ahmed Abdel Moneim, a 22-year-old student who has been sleeping in the square for days. "The French Revolution took a very long time so the people could eventually get their rights. ... If we have to spend our life to get rid of Mubarak, we will."
It's a sentiment shared by many in Tahrir Square, which at times feels like a bubble of optimism that the sheer will of youthful protesters can overcome all obstacles.
"Every day we sit out here, we gain against Mubarak," said Sharif Mohammed, an electrical engineer. "Maybe we'll be tired for a month, but we will be able to live in freedom for the rest of our life."
Beyond the square's tank-guarded gates, however, a decidedly more pessimistic view takes hold. Some ordinary Egyptians are upset that life has ground to a halt and will remain that way as long as there is no resolution in sight. The government has sought to fuel that image, with state TV and officials depicting the protesters as causing disorder, refusing reasonable concessions by the state and backed by meddling foreigners.
Recognizing the need to keep support among the wider public, protest organizers put out a statement Saturday denying all those claims. "The broad positive response by the people to our movement's goals reveals that these are the goals of the Egyptian masses in general, not any internal or external faction or entity," it said.
As the crisis drags on, the protesters also face the raw physical toll of camping out, night after night, in the sprawling public square. Hunger, illness and injuries might well become a drain.
Cairo's chilly winters could also make things very uncomfortable for all but the most dedicated activists. A misty drizzle on Saturday turned the once verdant patches of grass in the square where many people have pitched their tents to mud.
In the early afternoon, many protesters were just waking up after putting in long hours on the barricades keeping watch for nighttime attacks by regime supporters who assaulted the camp earlier in the week, sparking 48 hours of pitched battles.
Many of the men, however, who toss off their grimy blankets and brush the strands of dead grass off their increasingly muddy clothes look well-used to a hard life.
Throughout their campaign, the protesters have thrown together an impressive self-organization, with makeshift clinics to treat the wounded, security teams hunting out infiltrators and a steady supply of food, tea and cigarettes brought in by supporters and vendors.
It is easy to see, though, how the daily rigors of defending the square - the cat naps on patches of grass, the limited food, the stress of repelling attacks from stone-throwing and machete-wielding pro-government supporters - have taken their toll.
Scores of men with bandages on their heads or an arm in a sling roam the square. Others hobble around on a crutch or nimbly hold out scorched hands wrapped in gauze. The health minister says more than 1,200 people have been wounded in clashes since Wednesday.
Some of the difficulties the protesters try to turn to their advantage.
"The hunger spurs us on," said Omar Salim, who traveled to Cairo from the northern Sharqiya province and has spent the last four nights sleeping in the square. "We're in this together, we are all one - that's what keeps us going."
Then there is the higher price - at least 109 people have been killed in the protests since they began Jan. 25.
Ahmed Mustafa, a 58-year-old plumber, said his son, Islam, 26, was shot in the stomach in front of the Interior Ministry last Saturday.
"He was killed about 15 feet (5 meters) from where I was standing," Mustafa said. "I carried him out with the help of others and brought him here."
Despite his son's death - or because of it - Mustafa said he remains unflinching in his determination to fight on. "My sense of dedication only became greater and my screams louder," he said.
"This country has no freedom, no plurality of opinion," he said. "What kind of country is it in which a young man of 26 isn't able to marry, to make a family?"
In a sentiment echoed by many of the protesters on Tahrir Square, Mustafa said he and his two other adult sons - Karim, 27, and Khaled, 24 - are also ready to pay with their lives if it ensures the end of Mubarak's regime.
"They've come to die like him," he said. "And I'm ready to go, too."