People whose thoughts are overly influenced by fear are likely to be more attached to their own status and suffer from lack of self-confidence. They are so preoccupied with the threat of evil that they cannot see the opportunities that exist around them. This attitude is in contrast to the joyous outlook of those who are able to enjoy life as it is given them, without fear of judgement from their fellow man.
Fear can lead to the feeling that the world is a hostile place, filled with dangers, but this attitude is in contrast with the attitude of those who have learned that every person on earth is a neighbor and potential friend. Although the material world presents us with many challenges, heartbreaks, and catastrophes, it is the job of the spiritual person to see through the concealment to the hidden truth beneath it all: that God is good, that He cares about us, and that our daily toils to observe the mitzvot commanded to us, including loving our neighbor, will grant us genuine merit before the Throne of Judgement.
As was mentioned above, fear can lead to a person being overly concerned with his own status and being unable to see opportunities that exist before him. A person who fears for his own personal security is also too preoccupied with himself and his own interests to be able to pay attention to his neighbor. Indeed, fear can lead a person not only to neglect his own duties but to turn away from his neighbor as well.
This is the opposite of what we should be doing. We have been commanded to love our neighbor, not only because it is our duty but because it is our joy. We have been given the Torah for a reason: not just because it will bring us success in this world but because it will bring us joy in this world and eternal joy in the World to Come.
This joy can be taken from us only if we neglect our duties in order to focus on the things that have been placed before us as temptations or distractions. When we neglect our duties, we lose our joy.