SB 10.10.14

yathā kaṇṭaka-viddhāṅgo
 jantor necchati tāṁ vyathām
jīva-sāmyaṁ gato liṅgair
 na tathāviddha-kaṇṭakaḥ
Synonyms: 
yathā — just as; kaṇṭaka-viddha-aṅgaḥ — a person whose body has been pinpricked; jantoḥ — of such an animal; na — not; icchati — desires; tām — a particular; vyathām — pain; jīva-sāmyam gataḥ — when he understands that the position is the same for everyone; liṅgaiḥ — by possessing a particular type of body; na — not; tathā — so; aviddha-kaṇṭakaḥ — a person who has not been pinpricked.
Translation: 
By seeing their faces, one whose body has been pricked by pins can understand the pain of others who are pinpricked. Realizing that this pain is the same for everyone, he does not want others to suffer in this way. But one who has never been pricked by pins cannot understand this pain.
Purport: 

There is a saying, “The happiness of wealth is enjoyable by a person who has tasted the distress of poverty.” There is also another common saying, vandhyā ki bujhibe prasava-vedanā: “A woman who has not given birth to a child cannot understand the pain of childbirth.” Unless one comes to the platform of actual experience, one cannot realize what is pain and what is happiness in this material world. The laws of nature act accordingly. If one has killed an animal, one must himself be killed by that same animal. This is called māṁsa. Mām means “me,” and sa means “he.” As I am eating an animal, that animal will have the opportunity to eat me. In every state, therefore, it is ordinarily the custom that if a person commits murder he is hanged.