http://techcrunch.com/2013/04/20/cognitive-overhead/
Simple and straight to the point. I especially want to highlight the following from the article:
Make people work more, not less.
Put your user in the middle of your flow. Make them press an extra button, make them provide some inputs, let them be part of the service-providing, rather than a bystander to it. If they are part of the flow, they have a better vantage point to see what’s going on. Automation is great, but it’s a layer of cognitive complexity that should be used carefully. (Bump puts the user in the middle of the flow quite physically. While there were other ways to build a scalable solution without the physical bump, it’s very effective for helping people internalize exactly what’s going on.)
Give People Real-Time Feedback
If your user has to wonder, “So, did it work?” you’ve failed. Walk people through using your product like a magician leads the audience through an illusion. Point out the steps along the way, or whatever magic your product is providing could be lost to the user.
Slow Down Your Product.
We’ve all heard stories of Google’s relentless quest for search-result speed, but sometimes you need to let your user understand and appreciate what your service is doing for them. Studies have shown that intentionally slowing down results on travel search websites can actually increase perceived user value — people realize and appreciate that the service is doing a lot of work searching all the different travel options on their behalf.