Hashem already decided on rosh Hashana how much parnassah each person is going to make for the coming year BUT We need to still do our HISHTADLUS and the best HISHTADLUS we can do for parnassah is having sincere true Bitachon and Emunah in Hashem together with Tefilla.
If a person works on himself to reach this level of true Bitachon and Emunah DIRECTLY IN HASHEM then it will not be a lack of HISHTADLUS if he doesn’t go to work daily to support his family, cause he is already on such a high level and closeness to Hashem and knows so deep inside of him that in truth no matter how much or hard he works it really all comes directly from Hashem