Think good and it will be good -- The Power of Jewish Emunah
The idea of "think good and it will be good" is a very deep mystical idea related to the very essence of the Jewish soul.
The Maggid of Mezritch explains the power of emunah and bitachon based on Vayikra 25:18-21 (Parshas Behar)
יח וַעֲשִׂיתֶם, אֶת-חֻקֹּתַי, וְאֶת-מִשְׁפָּטַי תִּשְׁמְרוּ, וַעֲשִׂיתֶם אֹתָם--וִישַׁבְתֶּם עַל-הָאָרֶץ, לָבֶטַח
יט וְנָתְנָה הָאָרֶץ פִּרְיָהּ, וַאֲכַלְתֶּם לָשֹׂבַע; וִישַׁבְתֶּם לָבֶטַח, עָלֶיהָ
כ וְכִי תֹאמְרוּ, מַה-נֹּאכַל בַּשָּׁנָה הַשְּׁבִיעִת: הֵן לֹא נִזְרָע, וְלֹא נֶאֱסֹף אֶת-תְּבוּאָתֵנוּ
כא וְצִוִּיתִי אֶת-בִּרְכָתִי לָכֶם, בַּשָּׁנָה הַשִּׁשִּׁית
18. You shall perform My statutes, keep My ordinances and perform them, then you will live on the land securely.
19. And the land will then yield its fruit and you will eat to satiety, and live upon it securely.
20. And if you should say, "What will we eat in the seventh year? We will not sow, and we will not gather in our produce!"
21. [Know then, that] I will command My blessing for you in the sixth year, and it will yield produce for three years. 1
The Mezritcher Maggid writes that if the Jews peform the mitzvah of the Shmitta year with emunah and bitachon, then they do not need Hashem's blessing because they -- the Jews themselves -- will bring down the blessing of the land yielding its fruit and eating to satisfaction. Only if they are lacking in emunah and bitachon will they say "What will we eat in the seventh year?" and then they force Hashem Himself (so to speak) to bring the blessing on the land "I will command My blessing for you..."
In other words, the blessing a Jew brings down through his emunah is greater than the blessing that Hashem Himself sends down!
וע"י אמונה נתלבש בתוכו האמת וגורם פעולתו
States the Mezritcher Maggid: "By having complete emunah, this makes a vessel for emes which enclothes itself in the emunah and it causes the desired results."