The investing mistake most people make is not picking the wrong stocks — it is believing that getting investing right requires continuous active engagement in a market where the evidence consistently shows that active management underperforms passive indexing after costs and that behavioral interventions like market timing and performance chasing reliably reduce returns below what simply staying invested would produce. The strategy that outperforms almost everything — low-cost index funds, consistent contributions regardless of market conditions, automatic reinvestment, and infrequent rebalancing — requires almost no sophistication to implement and almost no engagement to maintain. Its primary challenge is behavioral rather than intellectual, and addressing that challenge is the most valuable thing most investors can do with their attention.