(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.

• be as stiff as a ramrod
• be as straight as a die
• be as straight as a ramrod
• be as strong as an ox
• be as stubborn as a mule
• be a star in the making
• be as thick as thieves
• be as thick as two short planks
• be as thin as all get out
• be as thin as a rake
• be as thin as a stick
• beast of burden
• be as tough as old boots
• be as ugly as sin
• be a sure thing
• be as white as a sheet
• be as white as snow
• beat about the bush
• beat a dead horse
• beat a hasty retreat
• be a tall order
• be at a loose end
• be at a loss
• beat a path to door
• beat a path to someone's door