No one else can share its joy

Proverbs 14:10 ¹⁰Each heart knows its own bitterness, and no one else can share its joy.--Bible

Hello,

Could anyone explain the words above? I don't understand why no one else can share its joy. If I am happy, it is easy for me to share my happiness with other people via telling them, inviting them to parties, etc.

Thanks!