There's a psychological phenomenon whereby people are more likely try to exit through the main entrance, or the one through which they entered the building, rather than use fire exits. This can cause significant and potentially life-threatening delays in evacuation.
This is affected by factors such as:
Presence / absence / thickness of smoke (absence of smoke = lack of urgency = people tend not to use fire exits)
Signage / wayfinding aids (e.g. low-level aids to finding fire exits)
Familiarity with the building
Group behaviour - which way is everyone else going? (and in particular which way are the other the members of a close group such as a family, going?)
There are other factors at work, such as familiarity with the escape route: research suggests that people are often more likely to use a familiar exit that is further away than an unfamiliar exit nearby – again increasing evacuation times. This was often attributed to panic, although social scientists now seem to agree that seemingly-irrational flight behavior to an exit is perfectly rational: they are rationally seeking out an exit with which they are familiar. Group dynamics also plays a part; how a number of people, in different states of fear, influence one another. Evidence suggests, for example, that people evacuate buildings alongside colleagues with whom they have an emotional attachment In a shopping centre that social dynamic may be familial, with parents trying to control small children. How does the family group react, when each member is instinctively responding in a different way?
Fire Dynamics & Human Behaviour, AJ Welch, 7 Jan 2015
People generally exit through the main entrance without the presence of smoke; in the presence of smoke they are more likely to use the fire exit, and low-placed signs facilitate the use of the fire exit nearest the evacuee. Further familiarity with [the building] was related to exit strategy; with less experience, people are more likely to exit via the main entrance, not the fire exit.
The Oxford Handbook of Environmental and Conservation Psychology, Susan D. Clayton, p.56