Not changing my fundamental mindset about money. 99% of the time, it's better to focus on the long-term goal of increasing your income, rather than saving a small amount of your current income. Extreme frugality is almost always a waste of time and earning potential.

For example: 15% of $150,000 is more than 40% of $50,000. This is also why living in a HCOL but making proportionally more money is financially smart. If you can only save 10% of your income, that 10% number will be far higher if your total salary is higher.