You asked for evidence backing up the statement &quot;People whose day job is to predict this stuff can&#x27;t even make good predictions&quot;. Managers of active mutual funds are exactly these people. The fact that they can&#x27;t beat the market is clear evidence they can&#x27;t make good predictions.<p>Of course you could say &quot;well, the good managers beat the market, even though on average they don&#x27;t&quot;. But you could also say that the few people who correctly predict three coin flips in a row are &quot;good at predicting coin flips&quot; - it&#x27;s easy to say this in retrospect but impossible to predict who the &quot;good ones&quot; are upfront.