Here are some reasons why:

1. Market Timing Risk: Trying to time the market by investing only at all-time highs is a form of market timing. It’s difficult, if not impossible, to consistently predict when the market will reach its peak or bottom. By waiting for all-time highs, you may miss out on opportunities to invest during periods of lower valuations.
2. Missed Opportunities: By staying on the sidelines and waiting for all-time highs, you may miss out on potential gains during market uptrends. Markets tend to trend upwards over the long term, and waiting for all-time highs could result in missing out on significant growth opportunities.
3. Increased Volatility: Investing only at all-time highs may subject your investments to increased volatility. Markets often experience corrections or pullbacks after reaching new highs, which could lead to short-term losses if you invest at the peak of a cycle.
4. Overvalued Investments: All-time highs may not always reflect the underlying fundamentals of the market or individual stocks. Investing when the market is at its peak could mean paying inflated prices for assets that may be overvalued, increasing the risk of potential losses if valuations revert to more reasonable levels.
5. Psychological Bias: Waiting for all-time highs to invest may be driven by psychological biases, such as fear of missing out (FOMO) or herd mentality. Making investment decisions based on emotions rather than fundamentals can lead to suboptimal outcomes.
6. Long-Term Perspective: Successful investing is often based on a long-term perspective rather than short-term market movements. By focusing on your investment goals, risk tolerance, and asset allocation strategy, you can build a diversified portfolio that can withstand market fluctuations over time.

Overall, investing only when the market is at an all-time high carries significant risks and may not be a prudent strategy for long-term wealth accumulation. It’s essential to focus on a disciplined investment approach, diversification, and staying invested through market cycles to achieve your financial goals.