What's a non-obvious sign that two partners are truly growing together, rather than just coexisting?

Have you ever done something adventurous that made you appreciate everyday comforts like walking on solid ground? What was it and why?
Why has the US stock market been unusually successful compared with almost every other country?
Do people who see kids as a "retirement plan" often end up disappointed, and why?
If your life were a song, what kind of message or feeling would it carry for the people who hear it?