Essentially it's this: Everyone's problems are as big as they are.
I would reasonably often have conversations that went something like this:
Friend: "Man, I feel lousy. I have a cold."
Jay: "Man, that sucks. I hope you feel better soon."
Friend: (embarrassed) "Oh, wait. You have cancer. Never mind."
For "a cold" substitute "a flat tire", "a job interview", "a sick dog", etc.
The thing is, the scale of my issues don't mean that anyone else's matter less. Yes, there is the question of perspective. I'm not an idiot, I understand there's a huge distinction between a three-day upper respiratory infection and a year of brutal treatments for a potentially fatal disease. But if you're not the one with cancer, the cold can be a pretty big problem. (If you're on chemo, a cold can be a gigantic problem, but that's a topic for another time.)
Sick or not, I am human too. I care about my friends and am sympathetic to their troubles. Often as not, it eases my mind to talk about some else other than FUCKING CANCER ALL THE GOD-DAMNED TIME. Even if that something else is tough stuff as well.
So, like I said, everyone's problems are as big as they are.
This applies in writing as well. Novelists worrying about their royalty statements are grappling with problems that are just as real to them as people aching to sell their first story. We just call that trading up to a better class of problems. If you haven't sold yet, the kvetching of established writers sounds like complaining about paying taxes on your lottery winnings. But guess what? Lottery winners pay taxes, too.
Cancer sucks. So does a head cold, a flat tire, etc. We all live our lives. I'm just trying to live mine.