It's the difference between surviving and thriving.
If there's a scale of 0-10 on mental health happiness scale, the low end would be actively worrying and thinking about things you wish were different, things you wished you had, things you hate about yourself and your life.
The middle would be a lot of 'meh' and just getting on with your day without much incident, not many highs and not many lows. The high-end is actively happy and fulfilled and enjoy looking to the future on a regular basis, and the lows aren't as low because you have that close support network in place.
This is generally speaking, and individually people can work around these things.