In the chapter on zehirut (watchfulness) and related traits, the Ramchal addresses the proper framework of human effort: one must make appropriate effort while recognizing that ultimate outcomes are in God's hands — excess worry or obsession with hishtadlut reflects a lack of bitachon.
אָמְנָם מָה שֶׁיּוּכַל לִשְׁמוֹר אֶת הָאָדָם וּלְהַצִּילוֹ מִן הַמַּפְסִידִים הָאֵלֶּה הוּא הַבִּטָּחוֹן, וְהוּא שֶׁיַּשְׁלִיךְ יְהָבוֹ עַל ה' לְגַמְרֵי, כַּאֲשֶׁר יֵדַע כִּי וַדַּאי אִי אֶפְשָׁר שֶׁיֶּחְסַר לָאָדָם מָה שֶׁנִּקְצַב לוֹ, וּכְמוֹ שֶׁאָמְרוּ זַ"ל בְּמַאַמְרֵיהֶם (ביצה ט"ז א): כָּל מְזוֹנוֹתָיו שֶׁל אָדָם קְצוּבִים לוֹ מֵרֹאשׁ הַשָּׁנָה וְגוֹ', וְכֵן אָמְרוּ (יומא ל"ח ב): אֵין אָדָם נוֹגֵעַ בַּמּוּכָן לַחֲבֵרוֹ אֲפִלּוּ כִּמְלֹא נִימָא. וּכְבָר הָיָה אָדָם יָכוֹל לִהְיוֹת יוֹשֵׁב וּבָטֵל וְהַגְּזֵרָה הָיְתָה מִתְקַיֶּמֶת, אִם לֹא שֶׁקָּדַם הַקְּנָס לְכָל בְּנֵי אָדָם, (בראשית ג:יט): בְּזֵעַת אַפֶּךָ תֹּאכַל לֶחֶם, אֲשֶׁר עַל כֵּן חַיָּב אָדָם לְהִשְׁתַּדֵּל אֵיזֶה הִשְׁתַּדְּלוּת לְצֹרֶךְ פַּרְנָסָתוֹ, שֶׁכֵּן גָּזַר הַמֶּלֶךְ הָעֶלְיוֹן. וַהֲרֵי זֶה כְּמַס שֶׁפּוֹרֵעַ כָּל הַמִּין הָאֱנוֹשִׁי אֲשֶׁר אֵין לְהִמָּלֵט מִמֶּנּוּ. עַל כֵּן אָמְרוּ (ספרי): יָכוֹל אֲפִלּוּ יוֹשֵׁב וּבָטֵל (יראה סימן ברכה) תַּלְמוּד לוֹמַר: בְּכָל מִשְׁלַח יָדְךָ אֲשֶׁר תַּעֲשֶׂה (דברים כח:כ). אַךְ לֹא שֶׁהַהִשְׁתַּדְּלוּת הוּא הַמּוֹעִיל, אֶלָּא שֶׁהַהִשְׁתַּדְּלוּת מֻכְרָח, וְכֵיוָן שֶׁהִשְׁתַּדֵּל הֲרֵי יָצָא יְדֵי חוֹבָתוֹ, וּכְבָר יֵשׁ מָקוֹם לְבִרְכַּת שָׁמַיִם שֶׁתִּשְׁרֶה עָלָיו וְאֵינוֹ צָרִיךְ לְבַלּוֹת יָמָיו בַּחֲרִיצוּת וְהִשְׁתַּדְּלוּת, הוּא מָה שֶׁאָמַר דָּוִד הַמֶּלֶךְ עָלָיו הַשָּׁלוֹם (תהלים עה:ז-ח): כִּי לֹא מִמּוֹצָא וּמִמַּעֲרָב וְלֹא וְגוֹ', כִּי אֱלֹהִים שׁוֹפֵט וְגוֹ' וּשְׁלֹמֹה הַמֶּלֶךְ עָלָיו הַשָּׁלוֹם אָמַר (משלי כג:ד): אַל תִּיגַע לְהַעֲשִׁיר מִבִּינָתְךָ חֲדָל. אֶלָּא הַדֶּרֶךְ הָאֲמִתִּי הוּא דַּרְכָּם שֶׁל הַחֲסִידִים הָרִאשׁוֹנִים, עוֹשִׂים תּוֹרָתָן עִקָּר וּמְלַאכְתָּן טְפֵלָה, וְזֶה וְזֶה נִתְקַיֵּם בְּיָדָם, כִּי כֵּיוָן שֶׁעָשָׂה אָדָם קְצָת מְלָאכָה, מִשָּׁם וָהָלְאָה אֵין לוֹ אֶלָּא לִבְטֹחַ בְּקוֹנוֹ וְלֹא לְהִצְטַעֵר עַל שׁוּם דָּבָר עוֹלָמִי, אָז תִּשָּׁאֵר דַּעְתּוֹ פְּנוּיָה וְלִבּוֹ מוּכָן לַחֲסִידוּת הָאֲמִתִּי וְלָעֲבוֹדָה הַתְּמִימָה.
However, that which can protect a person and save him from these detriments is trust in G-d. Namely, that a person casts his burden entirely upon G-d, knowing that it is certainly impossible for a man to lack what was designated for him, as our sages taught: "all of a person's sustenance [for the year] is fixed for him from Rosh Hashana [to Yom Kippur]" (Beitzah 16a). Likewise, they said: "no man can touch what was prepared for his fellow even to the extent of a hair's breadth" (Yomah 38b). A person could have sat idle and the decree would have been fulfilled (his designated portion would have come to him), had it not been preceded by the fine imposed on every human being: "by the sweat of your brow shall you eat bread" (Gen.3:19), whereby a person is required to make some effort for obtaining his livelihood, for thus the exalted King decreed. This is like a tax imposed on the human race which one cannot escape from paying. Therefore, our sages, of blessed memory, said (Sifri 15:18): "I might think one can sit idle, but scripture says (Devarim 28:20): 'in all that you set your hand to do' ". Only that it is not the efforts (hishtadlut) that help. Rather, the efforts are necessary, but once one has put in some effort, he has already discharged his obligation and there is place for the blessing of Heaven to rest upon him, and he need not consume his days in exertion and labor. This is what king David said: "For not from the east or from the west, nor from... but it is G-d who executes judgment, [putting down one and lifting up another]" (Tehilim 75:7-8), and king Shlomo said: "Do not weary yourself to grow rich; cease applying your understanding" (Mishlei 23:4). Rather, the true path is that of the "early Pious ones", who made their Torah primary and their work secondary, and succeeded in both (Berachot 35b). For once a man does a little work, from then on, he need only trust in his Master, and not be distressed by any worldly matters. Then his mind will be free and his heart ready for true Chasidut and perfect divine service.