For the source text click/tap here: Yevamot 12
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In determining who is a minor the Rabbis say: Both this one and that one, i.e., in all these cases, she may go ahead and engage in relations in her usual manner, and Heaven will have mercy upon her and prevent any mishap, since it is stated:
ב כִּי-הִטָּה אָזְנוֹ לִי; וּבְיָמַי אֶקְרָא.
2 Because He hath inclined His ear unto me, therefore will I call upon Him all my days
Ps 116:2
“The Lord preserves the simple”
The justification for engaging in dangerous activities is based on a halachic concept known as "shomer peta'im Hashem"[ which translates as, "God guards the unwise.
According to this principle, something which is considered to be a mainstream or routine activity is permitted to be performed even though it includes dangerous elements.
This is true as long as the risks involved are proven to be negligible.
We explore the halachic parameters of this notion and how much danger is acceptable in various situations.