To those self-doubters eternally irritated by their confident friends: rejoice. Eric Barker has just added excerpts from a new study to his blog, Barking Up the Wrong Tree, that show self-doubt can actually lead to better performance. So say researchers from Bangor University and Aberystwyth University in the UK.

They measured rope-skippers' achievements when made to doubt their abilities. Here's their conclusion:
Some self-doubt can benefit performance, which calls into question the widely accepted positive linear relationship between self-confidence and performance. As effort did not increase with decreased confidence, the precise mechanisms via which self-confidence will lead to an increase or a decrease in performance remain to be elucidated.