Fear
In a place with monsters ready to eat you at any moment, there will obviously be some fear. However, to get out of a situation more easily, that fear must at times be restricted. If you give in the fear and let it consume you, you will likely perish because you have no strength left to fight. The team from the cellar worked together throughout the movie to prevent anything seriously bad from happening, and this kept more people at ease.
Of course, Night of the Living Dead is a horror movie, meant to evoke fear of the audience. However, fear is an important lesson for viewers, showing that if you don't act purely on instinct, you are more likely to survive a disastrous situation like the one portrayed onscreen.
Trust
In times of trouble, it is easy to doubt someone, and this happens several times throughout the film. For instance, when Ben is outside and wants to get back into the cellar, Harry refuses to let him in. Harry's actions were likely motivated by fear, but in order to remain a strong group, there must be a sense of internal trust. If all of these people were out on their own, they probably would not have survived as long as they had.
In the final scenes when Ben is shot, the ranger responsible was not looking for anyone in particular, rater shooting haphazardly. Had he listened or watched the lively actions of Ben, he may have saved an innocent and brave soul.
Survival
In an apocalyptic scenario, most people are going to do what is best for themselves, rather than what is best for others. A primary instinct in humans is survival, but that doesn't mean it should overpower love, sympathy, and compassion. As time progressed and things became worse, the team was losing faith that they could survive. Many of them gave up, which is also not a good thing to do. Survival is often more complex than it is made out to be, and should neither be disregarded nor taken for granted.
