What mistakes do experienced investors still commonly make, and how can I avoid them?

Common mistakes include emotional reactions to market volatility, overtrading, chasing hot investments, neglecting diversification, ignoring fees, and failing to plan for taxes. Avoid timing the market and stick to a disciplined plan: set a long-term asset allocation based on your goals and rebalance periodically. Minimize costs by choosing low-fee funds and limiting unnecessary trading. Maintain emergency savings to prevent forced withdrawals. Use dollar-cost averaging for new contributions to reduce timing risk. Educate yourself on behavioral biases (loss aversion, herd behavior) and build guardrails: automated contributions, pre-set rebalancing rules, and a written investment policy that keeps emotions out of critical decisions.