Why does a good grinder matter more than an expensive machine?

Grind quality is the single biggest determinant of espresso quality. Inconsistent grind size (particle distribution) leads to uneven extraction — water finds the path of least resistance through coarser particles, leaving finer ones over-extracted. Even a $2,000 machine can't fix bad grind. The industry wisdom is: spend 50–60% of your espresso budget on the grinder. A $400 grinder + $400 machine will outperform a $100 grinder + $700 machine.