This "mindset" theory came from several studies in which researchers compared the effects of praise-for-intelligence ("You did well because you're smart") vs. praise-for-effort ("You did well because you worked hard") on public school students. They gave them a series of tests: an easy one, a hard one, and an easy one again. All were told they did well on the first test and poorly on the second. But on the third, those who thought their earlier success was due to smarts did worse than those who thought it was because they had worked hard. In addition, when later asked to write about the third test, these students lied about their scores, inflating them (whether intentionally or not is another question).
The takeaway was that it's harder to deal with failure if you think your intellectual ability is not related to effort but simply something you have or you don't. Other studies showed such participants actually avoid challenging activities in order to avoid risking failure and thus a blow to their self image. Ironically, this strategy backfires because challenges (and failure) lead to growth.
Dweck made sure her subjects were all good students beforehand so that differing ability wouldn't compromise the results. But an implication often drawn from the work is that we all have equal ability to start with and an attitude adjustment is all you need for success. With learning disabilities this obviously isn't true, but recent experiments with mice show that for the rest of us it may not hold either. A group of scientists (16 credited) in 2010 found a protein in the hippocampus (Greek for seahorse, because of it's shape--I just learned that last week) that interfered with long term potentiality (LTP), the process by which new information is (somehow) used in learning and memory. They couldn't find any positive reason for its presence, so developed some mice (whose brains are eerily similar to ours--shiver) who lacked this protein to see what would happen. Turns out they learned faster, with no discernible side effects. Wait; what? Does this mean the amount of this protein I have in my body affects how quickly I can do crosswords and such? Because if so, it means we don't all start with a level playing field, some of us are just naturally smarter than others. Not that your belief in your ability to improve won't help you in the long run; it will. It just won't get you into Mensa if that's not where you were going in the first place.
Hardly a radical discovery, I know, but it does take a bit of the wind out of the I-think-I-can sails, I think.
References
Praise for Intelligence Can Undermine Children's Motivation and Performance (Mueller & Dweck, 1998)
RGS14 is a natural suppressor of both synaptic plasticity in CA2 neurons and hippocampal-based learning and memory (Lee et al., 2010)