請問out of self-defense的意思

請問這句話裡的out of self-defense是什麼意思呢?

So it wasn't long before I felt obliged, out of self-defense, to get busy
filling the gaps in my knowledge of this extraordinary man and his body of
work.

是說:「出於自我防衛」,還是「缺乏自我防衛」
這裡的out實在不知道怎麼解釋,還請幫忙釋疑,感謝
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