Each heart knows it's own bitterness, and no-one else can share its joy (v10).
Everyone has a story.
As a pastor I have met many people and without exception, all are living with some level of disappointment. Each person had hidden in their heart a level of pain or frustration or unfullfilled desire.
Even those who seem most happy, sorted and content, once they let their guard down, had a heart that ached in some way. Without a doubt, the effect of Adam's rebellion has touched every life.
In contrast, most had an area of life they were deeply grateful for. Normally it was associated with their faith in Jesus ... or another key relationship.
We humans are complex beings; we live with the tension of bitterness and joy within our hearts. Only in heaven will this tension be released - then our joy will be unbounded and our hearts open and unguarded.
Until then we must lovingly listen to each others stories, even if we don't quite understand their pain.