• Tracking metrics is essential, but if you're not careful you can easily be misled.  Determine your true marketing end-goals, and measure against them.
• The metrics that mislead the most:  Email open rate/clicks, SEO ranking, click-thru rates on display advertising, and video views.
• The detailed and useful article gives you the metric that lies, the myth, what the metric actually measures, and how to avoid getting fooled.

From the article:

There is an old and not-very-funny joke about how half of all advertising budgets are flushed down the toilet; if only we, as advertisers, could figure out which half. Yeah, it's dumb, but it makes a compelling point. When it comes to digital marketing, the better you understand exactly what numbers spell the rise and fall of your business or brand, the better position you'll be in to understand how to keep your marketing dollars from ending up in the crapper. Unfortunately, there are plenty of metrics, still used every day, whose value should be seriously questioned because they might just be lying to you.