Retirement tax planning and the issue of underspending

Why is there so much confusion and disagreement on how much people need to retire comfortably? Partly it's an education issue and the result of a poor standard of financial literacy in general. I've worked with people earning seven figures who do not understand tax brackets. They think that if you earn over £125k, you pay 45% on everything, not just the bit above that threshold. These are accomplished people who are masters in their specific fields. But financial literacy is not taught in schools, and often parents do not know how to explain it either. As a result, we get a situation ...