Several common mistakes can derail an otherwise successful retirement. One major pitfall is underestimating expenses, particularly healthcare costs, which often rise significantly in later years. Another is withdrawing funds too aggressively in the early years of retirement (sequential risk), which can dangerously deplete the nest egg, especially if the market performs poorly. Failing to account for inflation, which can dramatically erode purchasing power over 20-30 years, is also a critical error. Additionally, many people neglect non-financial planning, such as finding a sense of purpose or maintaining social connections, which are crucial for happiness in retirement. Finally, lacking a clear strategy for withdrawals and tax management can lead to unnecessary financial strain.