The design purposefully focuses your attention on one thing in order to distract you attention from another. Most Dark Patterns use this trick in some way.
A good example is Australian low-cost airline jetstar.com:
To start off with, the site works pretty much as you'd expect. You do a search and pick the flights you want. Then you get to the seats page, below:
On the seats page, you can pick seats for an extra $5 each way, or you can skip seat selection at no extra cost. What's deceptive is the way this page presents your options: it uses misdirection to hide what is actually happening here.
When this page loads, they have already preselected a random seat for you. They use word-play trickery, as a "preselected" random seat here costs $5, but if you opt out via the tiny "skip seat selection" link at the bottom of the page, you're assigned a random seat without the $5 charge. There is no difference between the two options except in one case you pay $5 and the other you don't.
The misdirection at work here is the way they falsely make it look like an "opt in" process - after all, it's nonsensical to charge someone for selecting their own seat if they have not done so.
According to the Jetstar site, they run over 4000 flights per week - which works out as 208,000 flights per year. If every customer is caught out by this trick ($5 for a random seat), this accounts for over £1 million of profit each year.