Surplus money doesn't just sit around uselessly. It provides both self-insurance and an inheritance budget. So many unexpected things can happen. Market crash

Surplus money doesn't just sit around uselessly. It provides both self-insurance and an inheritance budget. So many unexpected things can happen. Market crashes, property damage or loss, health complications, need for unexpected long term care, a family member hits a life bump, etc. The peace of mind of being prepared, and the ability to solve unexpected problems without stress, protect one's quality of life. And any remaining surplus can go to loved ones, or a charitable cause one cares about. And you get budget flexibility too. Give oneself a raise later. Go on an unanticipated adventure with an unanticipated new love. Buy that 100 year old scotch for your 100th birthday! Given money (generally) grows exponentially, it doesn't take much surplus initially to accumulate a large surplus later. It is a huge opportunity loss to not plan for a surplus.