过去过不过的过去都会过去曾经忘不掉的曾经都是曾经
[guò qù guò bù guò de guò qù dōu huì guò qù céng jīng wàng bù diào de céng jīng dōu shì céng jīng]
Both parts of this sentence share the same theme - the transience of time. It reflects a mature attitude towards life that whether things in the past were difficult or painful, all memories will become mere recollections ultimately, emphasizing acceptance and letting go, possibly from someone with abundant experiences and stories in life.