✔ 最佳答案
This sentence means that they (basically) did not know that caring for an animal requires the level of commitment that they experienced.
They were not ready for the commitment because they simply don't know that the commitment is so great.
The "simply" is used to emphasize that this is the root cause (the very basic explanation) and that there are no other reasons why they were not able to live up to the commitment in looking after an animal.
They simply did not know that it takes so much work.
Does this help? Let me know if you have questions.
圖片參考:
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