It is not that fear causes indolence, but rather that indolence causes fear (Mesilas Yesharim, Chapter 9).
With this statement, Rabbi Luzzato makes a very important psychological point: we often deceive ourselves by reversing cause and effect. How many times have we heard (and said): "I am afraid to do so and so because ..."? We convince ourselves that this thought is the truth, while the real reason is that we are lazy. However, since we do not wish to admit laziness, we rationalize that the fear of some danger is keeping us from taking action.
I have seen many young people, who are reluctant to go on with their education or undertake any constructive course, become "drifters." They attribute their problem to indecisiveness or anxiety. Analytical oriented therapists may spend many fruitless hours trying to discover the psychological roots for their indecisiveness and anxiety. Cognitive psychotherapists, who urge them into action first and deal with the underlying factors later, have much better success. Why? The indecisiveness or anxiety is not the cause, but merely an excuse these young people give themselves to cover up their indolence.
Luzzato's Path of the Just is both a great work of ethics and a treasury of psychological wisdom. As the author says in the introduction, it is a book that should not only be studied and thoroughly digested, but re-read many times. Group study and discussion of this great work are particularly enlightening.
Nothing can be so misleading and hence destructive to our lives as self-deception. Serious study of Path of the Just accomplishes two things: (1) the mitzvah of Torah study, and (2) invaluable lessons about how to avoid self-deception.