Based on the writings of Rav Chaim Cohen, the Chalban, Tallelei Chaim, Sefer Bereishis, P. 538. There is no guarantee for the tzaddikim in this world. The tzaddik believes in Hashem's promise when He promises, but the tzaddik is not confident in his own ability to hold up on his end of the bargain, and thus deserve the promise. Hashem wants us to take full responsibility to act in this world, as if Hashem wasn't there to help. The root of this issue of bitachon (trust) is the paradox of yediah (Hashem's knowledge) and bechira (man's free choice). Rebbe Nachman says that this paradox comes from the chalal hapanui (the Empty Space). The greatest mysteries are revealed to us as great contradictions and paradoxes. Rebbi Akiva survived the experience in the pardes (orchard) because he was able to handle the paradox of the water. The closer you get to the King, the more guards there are. All contradictions are unified in the Ain Sof.