(one's) heart isn't in it
One is not emotionally invested in something. I used to love running, but my heart just isn't in it anymore—that's why I quit the track team this year. I can tell by the way you wrote this that your heart wasn't in it. Is something distracting you?
your heart isn't in something
If your heart isn't in something you are doing, you are not enthusiastic about it. Note: The heart is traditionally regarded as the centre of the emotions. Playing was no longer fun. I lost my competitiveness and my heart wasn't in it. She was a successful teacher, popular with her pupils and her colleagues, but her heart wasn't in it.