People sabotage their own chances in advance just to protect their self-image
In a 1978 study, Steven Berglas and Edward Jones found that after succeeding on a test through luck rather than skill, many participants chose to take a performance-impairing drug before a second test, handing themselves a built-in excuse. This 'self-handicapping' protects self-esteem: a loss can be blamed on the handicap instead of on a lack of ability.