In Bereshas 3:1-3 we see that because Chava added a chumrah she caused destruction to the world.
Hashem warned Adam and Chava not to eat from the tree of knowledge.
The Torah goes into detail of the conversation between the snake and Chave:
וְהַנָּחָשׁ֙ הָיָ֣ה עָר֔וּם מִכֹּל֙ חַיַּ֣ת הַשָּׂדֶ֔ה אֲשֶׁ֥ר עָשָׂ֖ה יְהֹוָ֣ה אֱלֹהִ֑ים וַיֹּ֙אמֶר֙ אֶל־הָ֣אִשָּׁ֔ה אַ֚ף כִּֽי־אָמַ֣ר אֱלֹהִ֔ים לֹ֣א תֹֽאכְל֔וּ מִכֹּ֖ל עֵ֥ץ הַגָּֽן׃
Now the serpent was the shrewdest of all the wild beasts that the LORD God had made. He said to the woman, “Did God really say: You shall not eat of any tree of the garden?”
וַתֹּ֥אמֶר הָֽאִשָּׁ֖ה אֶל־הַנָּחָ֑שׁ מִפְּרִ֥י עֵֽץ־הַגָּ֖ן נֹאכֵֽל׃
The woman replied to the serpent, “We may eat of the fruit of the other trees of the garden.
וּמִפְּרִ֣י הָעֵץ֮ אֲשֶׁ֣ר בְּתוֹךְ־הַגָּן֒ אָמַ֣ר אֱלֹהִ֗ים לֹ֤א תֹֽאכְלוּ֙ מִמֶּ֔נּוּ וְלֹ֥א תִגְּע֖וּ בּ֑וֹ פֶּן־תְּמֻתֽוּן׃
It is only about fruit of the tree in the middle of the garden that God said: ‘You shall not eat of it or touch it, lest you die.’”
Hashem told Adam and Chava not to EAT from the tree, but Chava added another layer of protection for herself, she took on a chumrah not to touch the tree either.
When questioned about Hashem’s command, Chava told the serpent that they cannot EAT OR TOUCH the tree.
According to Rashi, the serpent pushed Chava into the tree in order for her to touch it. The serpent said to her “see you did not die.” This led Chava to eat from the tree, causing her to be banished from Gan Eden and she brought death to the world.
We so clearly see from this story why the Torah warns us not to add anything onto the mitzvahs of the Torah something that was not commanded to us by Hashem, as this will lead to destruction of the world and our future generations.
See Devarim Chapter 13 pasuk 1
אֵ֣ת כָּל־הַדָּבָ֗ר אֲשֶׁ֤ר אָֽנֹכִי֙ מְצַוֶּ֣ה אֶתְכֶ֔ם אֹת֥וֹ תִשְׁמְר֖וּ לַֽעֲשׂ֑וֹת לֹֽא־תֹסֵ֣ף עָלָ֔יו וְלֹ֥א תִגְרַ֖ע מִמֶּֽנּוּ
Everything I command you, that you shall be careful to do it. You shall neither add to it, nor subtract from it.
The Gemara adds that if you add to the Torah, in the end, the adding will lead you to subtracting, as we see the case with Chava.
