For us who are of baby boomer age, it is humbling to be a beginner at anything. Playing guitar, writing, painting, speaking a new language--it doesn't matter. The image of the successful gray-hair is to be wise and to have learned life's secrets. So to keep that image we must stick to what we know or think we know. The wonder of a child discovering new aspects of the world is not so appealing in someone whose face is wrinkled, though I'm not sure why.
Having a beginner's mind means always being willing to learn. There is so much I want to learn I don't think I'll ever get to it all. Thank goodness I've become quite adept at saying "I don't know how to do this" and "I'm a beginner."
Being a beginner is a relief in many ways. Once I announce that I don't know, expectations of others are gone. Not being the expert is freeing. I'm tempted to not know anything at all about everything forever, but that wouldn't really work.
Learning something new brings a sense of growth and accomplishment. As long as we're growing we're not just dying.
If you are working on your increasing your own happiness, try learning something new. Maybe just something small everyday.