"You can do it, just believe in yourself!" = Sweet, but ineffective.

As humans, we're always sitting on a Kilimanjaro-like pile of boxes. The boxes consist of everything that has ever happened to us that contributes to our self-esteem.

In my pile, there is a Muay Thai box telling about the time the head trainer called me a baby when I laid stretched out on the ground after not being given a break for 20 minutes (the sadist). Nevertheless, this gives me a humble look at my Muay Thai abilities.

Your self-esteem did not fall out of the sky into your brain, the degree to which you believe in yourself depends on what information is contained in your pile of boxes.

If we are telling someone with low self-esteem to believe in themselves, the logical answer would be: "But what about all these boxes?"

In this metaphor, we build self-esteem by:

• Contributing to the pile with new boxes containing positive information.
  Affirming you can do it is more effective than believing you can do it.

• Tidying up by removing the boxes containing negative information. My idea of my physical strength is based on the thousands of deadlifts I've done, not on that (stupid) classmate calling me weak fifteen years ago.
  Self-esteem should be built on experiences that contextually matter.

I stimulate self-esteem in my Personal Training clients by letting them lift weights, not by telling them they are strong.

Credible Self-Esteem > Blind Self-Belief

Shortly (but still metaphorically) put, don't ignore someone's pile of boxes by blindly believing in them. Go through it and clean it up.