<span>An expert is someone who expends the least amount of energy for the greatest result.
We call a person an expert if he performs really perfectly as compared to the newcomers because he is highly trained and professional and has the abilities to a specific art. Expertise is usually measured on the basis of intelligence and activeness together. Experts can never be seen unconfident in doing their job.
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The backpack's main force that it it is exerting on the body's back and hips is coming from gravity, and can pull the spine downwards. This is why it's important to ear both straps.
