When you say "I didn't have the heart to tell him [insert uncomfortable truth here]", it means that you didn't say it because it would have hurt their feelings in some way. That seems a little bit backwards; in any other context, being sensitive about someone's feelings is having "a big heart" or "too much heart," and being "heartless" is being insensitive and not caring about others. So why does the heart metaphor seem to be backwards in this particular expression?
2possible duplicate of Meaning of "little heart" vs. "less heart"? and why (see oerkelens' answer).– Edwin AshworthAug 14, 2015 at 15:47
1@EdwinAshworth, that's a different definition of heart than the OP's question, though informative in its own right.– Kristina LopezAug 14, 2015 at 15:59
1IMO, "big heart" is more about generosity than sensitivity. A "tender heart" seems more in line with someone who is empathetic and considerate of others' feelings.– Kristina LopezAug 14, 2015 at 16:20
3The most literal translation would be "I didn't have the courage to tell him", but that literal translation misses the point that "telling" would likely somehow emotionally injure "him", and "I" would like to avoid that, possibly out of consideration of "him", possibly to avoid being "the bad guy" myself, possibly both.– Hot LicksAug 14, 2015 at 16:21
@Kristina Lopez 'he has even less courage (heart)'– Edwin AshworthAug 14, 2015 at 16:55
Another definition of "heart" is courage. So in that expression, someone is saying, in other words, they did not have the courage to tell him (uncomfortable truth).
Definition #4c of heart from MW-O:
4: the emotional or moral as distinguished from the intellectual nature: as
c: courage, ardor ex. never lost heart
From the Online Etymology Dictionary, a timeline of the various uses and phrases including "heart":
Old English heorte "heart (hollow muscular organ that circulates blood); breast, soul, spirit, will, desire; courage; mind, intellect," from Proto-Germanic *herton- (cognates: Old Saxon herta, Old Frisian herte, Old Norse hjarta, Dutch hart, Old High German herza, German Herz, Gothic hairto), from PIE *kerd- (1) "heart" (cognates: Greek kardia, Latin cor, Old Irish cride, Welsh craidd, Hittite kir, Lithuanian širdis, Russian serdce "heart," Breton kreiz "middle," Old Church Slavonic sreda "middle").
Spelling with -ea- is c. 1500, reflecting what then was a long vowel, and the spelling remained when the pronunciation shifted. Most of the modern figurative senses were present in Old English, including "memory" (from the notion of the heart as the seat of all mental faculties, now only in by heart, which is from late 14c.), "seat of inmost feelings; will; seat of emotions, especially love and affection; seat of courage." Meaning "inner part of anything" is from early 14c. In reference to the conventional heart-shape in illustration, late 15c.; heart-shaped is from 1744.
Heart attack attested from 1875; heart disease is from 1864. The card game hearts is so called from 1886. To have one's heart in the right place "mean well" is from 1774. Heart and soul "one's whole being" is from 1650s. To eat (one's own) heart "waste away with grief, resentment, etc." is from 1580s.
2Absolutely. And it's a usage which seriously predates Modern English. Aug 14, 2015 at 15:46
2But that's not what the expression means. "I didn't have the courage to tell him" has to do with avoiding an awkward situation and/or reprisal (your mention of an "uncomfortable truth" would be spot-on), whereas "I didn't have the heart to tell him" has to do with avoiding causing disappointment or sadness. Has the meaning of the expression changed over time? If so, why? (Is it due to a strange sort of influence from the other uses of "heart" that the OP refers to?)– ruakhAug 15, 2015 at 0:25
It may mean this in some ways Ruakh because upsetting a person may circumstantially lead to frightful consequences and simply causing heartbreak is a repercussion that may be feared by sympathetic folk on its own. Still, I concur that this isn't the primary sense of the phrase, despite McGraw's entry. I've been struggling to come up with an answer to this question since Heart is a very equivocal & important English word. I believe you need to understand most of the meanings to completely understand the phrase, rather than just any single one, which is difficult to do in Q. & A. format.– TonepoetAug 15, 2015 at 16:14
The feeling that I get from this phrase is more like
I didn't have the heartlessness to tell him.