Missing by Tim Kadlec

Data can blind you:

As Andy Davies puts it, “Site analytics only show the behaviour of those visitors who’ll tolerate the experience being delivered.” Sessions like this are extremely unlikely to ever show up in your data. Far more often than not, folks are going to jump away before analytics ever has a chance to note that they existed.

And later:

We build an experience that is completely unsuable for them, and is completely invisible to our data...we look at the data and think, “Well, we don’t get any of those low-end Android devices so I guess we don’t have to worry about that.” A self-fulfilling prophecy.