In this great presentation from TED, Dan Ariely demonstrates how easily we are guided into making specific decisions, all while being under the illusion of being in control (not me of course :).

Here are some of the highlights, excuse the crappy screenshots (the entire 17 minute video is embedded below).

In a survey among different countries the percentages of people willing to donate their organs varied quite a bit:

When checking to see why there were such differences between countries, they checked for cultural differences between countries and saw there was no correlation (Austria and Germany for example are culturally similar but have totally different percentages of organ donors).

The answer came from checking the donor form at the DMV.
In some countries (the ones with the low organ donor rate) there was a section like this in the form:
People wouldn't read the text, not check the box, and not join the organ donor program.

In other countries the same question would appear but with a slight variation:
and people would also not read the question, not check the box, but by doing so they would join the organ donor program.
(This is a classic opt-in vs. opt-out decision used in almost all online forms)

Another example he gives is in this sign up form for a newspaper:
1. is a web only subscription
2. is a print only subscription
3. is both web and print subscription for the exact same price as option 2

When presented with these 3 options, these were the percentages of people's choices:

So the middle option is useless (nobody chose it) and can be removed, right?
Look what happened when it was removed and only option 1 and 3 were offered:

So by offering a "useless" option, that nobody chose, the perceived value of the third (more expensive) option went up and more people chose it (because they believed they were getting more for the same price).
That "useless" option made more people pay $125 instead of $59.

Not bad, ah?

Check out the entire video: