曾经最掏心所以最开心
[céng jīng zuì tāo xīn suŏ yĭ zuì kāi xīn]
The phrase translates to 'Because I Gave My Heart Outmost In The Past, So I Was The Happiest'. It speaks of cherishing past happiness derived from wholeheartedly giving to someone else. Reflects positive memories associated with genuine affection.