"Why are you so rich ?!"
Normally this is the type of comment you're probably not supposed to respond to on the Internet, but on the off-chance I can impart some life-wisdom, here goes:
Because I was anything but well-off growing up, and I committed myself to making life choices that enabled a degree financial security (e.g., academics, self-study, etc.).
Because I've pursued a career in engineering and worked my way up to a Principle...