Yes, confidence is contagious but so is lack of confidence. My self-confidence won't cross the line into over-confidence or arrogance state.
I used to lack of any self esteem or confidence when I was in my secondary school days. Felt like a wimp with people walking all over you, take advantage or just ignore you. Whatever I needed to do something, I asked. Afraid, I might made any error. On the street, I'm was intimidated of being seen simply because I thought my clothes looked dreadful.
My life had no meaning. I was unhappy, self destructive, unsatisfied and aggressive.
All that changed after I had my first job, in shipping. I was given the opportunity by my boss and his faith in me is even more crucial than confidence.
If back then, I would never have written any blog, afraid my English, vocabulary, grammar and writing skills cannot make it.
But now, I DON'T REALLY CARE!
Seriously, faith and confidence are an unconquered army. It's how the way you look at and feel about yourself.
Take a look at the picture below.

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