Being Afraid Brings Fears

Question

A few Rabbonim mentioned in shiurim on TorahAnytime the concept that being constantly afraid of something tragic happening to oneself can bring about its fulfillment. Where do we find such a concept of Hashem eventually sending people whatever negative events they are afraid of occuring?

Answer 1

Proverbs 10:24 (translation following Rashi):

מְגוֹרַ֣ת רָ֭שָׁע הִ֣יא תְבוֹאֶ֑נּוּ וְתַאֲוַ֖ת צַדִּיקִ֣ים יִתֵּֽן׃‏

The fear of the wicked person will come upon him, but the desire of the righteous is granted.

Rashi also brings an example:

מגורת רשע. מה שהוא ירא יבא לו דור הפלגה יראו ואמרו (בראשית י) פן נפוץ וסופן כתיב ויפץ ה' אותם משם (שם):‏

The people who built the Tower of Babel did so because they were afraid of being dispersed, but the result of building it was that they were dispersed.

Answer 2

The Gemara (Pesachim 110b) states in a discussion about the dangers of demons (that harm a person as a result of doing things in pairs of two):

כללא דמילתא כל דקפיד קפדי בהדיה ודלא קפיד לא קפדי בהדיה

The rule of the matter is that all who are particular about pairs, the demons are particular with him; and if one is not particular, they are not particular with him

Answer 3

The main idea likely being referred is the inyan of אל תפתח פה לשטן (don't open your mouth to the Satan). That is, because someone voices a fear they have, the Satan may aid in bringing it to reality. Two sources for this (see here), one of which was brought in by @b-a from Bereishis 11:4 is:

וַיֹּאמְר֞וּ הָ֣בָה ׀ נִבְנֶה־לָּ֣נוּ עִ֗יר וּמִגְדָּל֙ וְרֹאשׁ֣וֹ בַשָּׁמַ֔יִם וְנַֽעֲשֶׂה־לָּ֖נוּ שֵׁ֑ם פֶּן־נָפ֖וּץ עַל־פְּנֵ֥י כָל־הָאָֽרֶץ׃

And they said, “Come, let us build us a city, and a tower with its top in the sky, to make a name for ourselves; else we shall be scattered all over the world.”

Of which the scattering was decreed upon them.

Similarly in Shemos 14:11:

וַיֹּאמְרוּ֮ אֶל־מֹשֶׁה֒ הַֽמִבְּלִ֤י אֵין־קְבָרִים֙ בְּמִצְרַ֔יִם לְקַחְתָּ֖נוּ לָמ֣וּת בַּמִּדְבָּ֑ר מַה־זֹּאת֙ עָשִׂ֣יתָ לָּ֔נוּ לְהוֹצִיאָ֖נוּ מִמִּצְרָֽיִם׃

And they said to Moses, “Was it for want of graves in Egypt that you brought us to die in the wilderness? What have you done to us, taking us out of Egypt?

Of which their burial in the desert was decreed on them.

Additionally, there are a few pesukim in the Tochachos that allude to this idea, like Devarim 28:60:

הֵשִׁ֣יב בְּךָ֗ אֵ֚ת כָּל־מַדְוֵ֣ה מִצְרַ֔יִם אֲשֶׁ֥ר יָגֹ֖רְתָּ מִפְּנֵיהֶ֑ם וְדָבְק֖וּ בָּֽךְ׃

He will bring back upon you all the sicknesses of Egypt that you dreaded so, and they shall cling to you.

And Rashi there:

אשר יגרת מפניהם: מפני המכות כשהיו ישראל רואים מכות משונות הבאות על מצרים היו יראים מהם שלא יבואו גם עליהם, תדע שכן כתיב (שמות טו כו) אם שמוע וגו' כל המחלה אשר שמתי במצרים לא אשים עליך, אין מיראין את האדם אלא בדבר שהוא יגור ממנו:

which you dreaded: [You dreaded] those diseases [not that you dreaded Egypt]. When Israel saw the extraordinary plagues that befell Egypt, they were afraid of them, i.e., they were afraid that these plagues would befall them too. You should know, [that the Israelites dreaded the plagues of Egypt,] because it is written,“If you hearken…, all the sickness that I have visited upon Egypt, I will not visit upon you” (Exod. 15:26) [implying that if you do not hearken, I will place them upon you! Since Israel feared those plagues, God used them as a threat, because] one can instill fear into a person only through something he fears.

Answer 4

מועד קטן כז ב

ואמר רב יהודה אמר רב לכל המתקשה על מתו יותר מדאי על מת אחר הוא בוכה ההיא איתתא דהות בשיבבותיה דרב הונא הוו לה שבעה בני מת חד מינייהו הוות קא בכיא ביתירתא עליה שלח לה רב הונא לא תעבדי הכי לא אשגחה ביה שלח לה אי צייתת מוטב ואי לא צבית זוודתא לאידך מית ומיתו כולהו לסוף אמר לה תימוש זוודתא לנפשיך ומיתא

Moeed Katan 27:b

Rav Yehuda said: whoever mourns for his dead too much, he will mourn for another dead. A woman was a neighbor of Rav Huna, she had seven sons and one died. She mourned in exaggerated manner. Rav huna sent to here :"Don't do like this". She didn't mind him. He sent her "If you would listen, good, If not you will have to prepare shrouds ". [she didn't listen] and all her sons died. eventually he told her, get shrouds for yourself and she died.

Maybe also:

ברכות יט א

ארשב"ל וכן תנא משמיה דרבי יוסי לעולם אל יפתח אדם פיו לשטן ואמר רב יוסף מאי קראה שנאמר (ישעיהו א, ט) כמעט כסדום היינו מאי אהדר להו נביא שמעו דבר ה' קציני סדום

Berchot 19:a

Rabbi Shimon ben Lakish said, and it was also taught in the name of Rabbi Yosei: One must never open his mouth to the Satan And Rav Yosef said: What is the verse from which it is derived? As it is stated: “We should have almost been as Sodom, we should have been like unto Gomorrah” (Isaiah 1:9), after which what did the prophet reply to them? “Hear the word of the Lord, rulers of Sodom; give ear unto the law of our God, people of Gomorrah” (Isaiah 1:10).