It's all about perspective. To really understand what someone is going through or feeling, you have to have experienced it. No matter how sensitive, kind, or well meaning, you cannot truly understand unless you have been in that same place of pain, of that kind of sorrow.
You cannot expect someone to feel a certain way, based upon your perception or assessment of their situation. To disregard or dismiss someone's sadness, their personal feelings, is disrespectful and beyond hurtful.
When someone is going through a difficult time, they don't need to be told to "cheer up" or "be strong". They need to be told they are cared about. They need to be validated, that their concerns and feelings matter. We need to respect what they are feeling and their right to feel it.
Each of us has a different path in life, a personal journey. We do not all have the same experiences. Some of us seem to have it easier than others, seeming to sail through life on fair winds and following seas. Others do not, forever struggling against a strong current under stormy skies.
Sometimes we choose our path. Sometimes it is laid out before us by someone else. There does come a time to chart our own course or at least the way we must navigate it, perhaps that being our journey.