The following is a fundamental lesson on the interrelationship between bitachon and hishtadlus:

A person should understand that as he lessens his business dealings and strengthens himself in his bitachon, so will his need for exertion be lessened….

[On the other hand], the more a person increases his hishtadlus and plunges into those efforts and makes them primary in his mind, correspondingly, Hashem provides his livelihood only after he exerts much effort!

~ The Beis HaLevi on Bitachon