isn't

someone's heart isn't in something

if someone's heart is not in something that they are doing, they are not very interested in it. She was studying law, but her heart wasn't in it and she gave up after a year.

See also: heart

there isn't a [mean, jealous, unkind etc.] bone in someone's body

he/she doesn't have a [jealous, mean, unkind etc.] bone in his/her body - something that you say in order to emphasize that someone is not jealous, mean, unkind etc.. She wasn't the possessive type, and there wasn't a jealous bone in her body.

See also: body, bone, there, unkind

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your heart isn't in it

you do not feel something is exciting or interesting enough to do. I tried to do some writing, but my heart wasn't in it.

Usage notes: sometimes used in the form your heart isn't in something: His heart isn't in supervising people.

not have the stomach (for something)

See also: heart