Finally, we might not help others because we assume they can help themselves.
For example, if someone on the sidewalk seems to be lost, people may think that he or she can find the necessary information without their help. This is especially true today since many people have smartphone with instant access to online maps.
Age is another factor. For instance, people would probably help an old man who accidently falls down on the sidewalk, but if a young man falls, they might do nothing. This happens because they think he can get up by himself.