above all else, above any skill or experience or clever plans or immunity, what keeps the survivors alive is luck.
being approached by the chopper pilot in No Mercy. finding the armoured truck completely abandoned and in mint condition in Crash Course. a boat waiting to evac survivors at the river even after the fall of Riverside in Death Toll. getting to the abandoned, bombed airport in time to fuel and board the plane in Dead Air. crashing in/near Allegheny National Forest that still has a military evac spot nearby in Blood Harvest. escaping Millhaven in a series of incredibly lucky events. finding a well-stocked sailboat in The Sacrifice.
it's when their luck finally runs out that gets someone killed. when, unluckily, the bridge starts off lowered; when, unluckily, one of the bridge generators fails.
the same applies to the second game as well.
Whitaker still being in his gun shop and finding Jimmy Gibbs Jr's car in the mall in Dead Center. the Fairfield Survivors still being at the bridge in The Passing. the Midnight Riders leaving a fully-prepped concert behind in Dark Carnival. Virgil still evacuating survivors from the Plantation House in Swamp Fever. Virgil spotting the Burger Tank sign in time in Hard Rain. getting to the bridge just before it's fucking blown up in The Parish.
and this is why I'm so pessimistic about the general fate of the population. you need to have weaponry and know how to use it, to be fit and healthy enough to endure extended strenuous activity, to be a Carrier which we know is rare, AND to have at least one teammate who also possesses all of these aspects, to survive. missing even one of these aspects will almost definitely get you killed unless you can fix it quick. but even if you get astronomically lucky enough to have all of them...and get even slightly unlucky once along the way?
well, just look at what happened to Bill.
in this zombie apocalypse, survival is luck-based, and, well...seven is a lucky number. looks like most of our protagonists hit the lottery, eh?