R'Eliyahu Dessler on Bitachon & Hishtadlus

In his classic monumental work,"Michtav M'Eliyahu"
R'EEliyahu Dessler ztvk"l presents a unique hashkafic view of Bitachon {what I would humbly translate as: one's "absolute security in the fact that H-Shem is the sole Director of one's fate"}vis à vis Hishtadlus {for which I humbly offer: "one's [required] effort in attaining... (the ellipsis indicating whatever it is one is attempting to gain).
In this instance,the Hishtadlus is pertaining to one's livelihood.

The reason for the need for Hishtadlus,writes R'Dessler,stems from Adam's sin.Prior to that, there was no necessity for Hishtadlus whatever, as everything was provided; thus,the entire concept is a "punishment and a curse"- as the Torah declares in Genesis:
"By the sweat of thine brow shall ye eat bread".R'Dessler quotes the Mesilas Yeshorim (Ch.22)which defines Bitachon as "the secure knowledge that it's impossible for one's income to be less than that which was decreed"
(referring to our belief that all one's income is decreed by Heaven on Rosh HaShana).