Sometimes written words cannot express one's feelings and emotions clearly until spoken. Because when we speak, there is the tone and mood of the speaker, to state an example, if you want to meet someone but you cannot make it and you said: "Another day lah." The "lah" if using hanyu pinyin tone (spelled-out sounds) it can mean frustration if it is the third sound but it can mean relaxing and casual tone if it is the fourth sound.
And sometimes written words may cause misunderstanding cos you didn't hear the tone or see the facial expression of the speaker which is why nowadays SMS or Whatsapp messages can cause a lot of misunderstanding if misinterpret.
Got it? Hee hee