Measuring is different than Succeeding

Many marketing executives believe in measuring effectiveness.  From Google Analytics to Conversion Tracking to "Share of Voice", the importance of measurements is growing rapidly.  In order to succeed though, we marketers have to actually do something with the data.  Make more rational decisions.  Invest more deeply in the  things that work.  Why would any rational person want to invest in something they know doesn't work?  And without measurement, why would any rational person invest in something they don't know if it works or not?