The Thinking Behind The Tweet

Self-confidence is built, over time, as stressful thoughts and situations are faced and dealt with. 

'Stressors' bring learning experiences that test self-confidence. The capacity to handle situations expands with experience. As increasingly-stressful learning experiences are handled, self-confidence grows. 

Without successful handling of stressors self-confidence has no chance to grow.

[Avoidance may provide relief  but it works against self-confidence.]

[Unsuccessful efforts at handling stressors may injure self-confidence...but, only if you let it...failures provide the opportunity to figure out 'better ways'...sooner or later 'better ways' lead to successful outcomes and then self-confidence grows.]