"The more a person lacks Knowledge, the more annoyed and bothered about his search for income." (Rabbi Nachman of Breslov, Likutey Moharan I, 56)
Comment: A person who does not have Knowledge (that is to say that he does not recognize that Hashem created the world and manage it) puts the search of income (parnasa) as a top priority of his life. Moreover, his lack of Knowledge removes the barriers of restraint in his desire to accumulate goods. This two factors create the ideal situation desired by the forces of evil: to increase stress in the lives of people and let them concentrate on something other than the Divine.
In contrast, the person who has a certain Knowledge admits that everything is decided by the Master of the world. Obviously, each individual must do his utmost to obtain a source of income that allows him to live a decent life. However, this person never forgets that the successes and failures are determined in Heaven. Therefore, he accepts with joy the income that is available to him: no matter if it is important or small.