What is "trust in G-d?" It is the realization that there are no accidents in the world, and that all aspects of a person's life are guided by the Almighty. This includes life and death, food, clothing, children, job, house, and health. Trust in G-d requires that a person accept the will of G-d in all these areas since he knows that whatever the Almighty does is for his ultimate good. In this way, the person who trusts in G-d will constantly have peace of mind.
A person without trust in G-d, however, will tend to suffer even when things are going well - because of anxiety about the future. About such a person, King Solomon said in Proverbs: "All the days of those poor (in wisdom) are unhappy ones."
(see Chovos Halevovos 4:4,5; Chazon Ish - Emunah u'Bitochon 2:1; Gateway to Happiness, p.81-2)