To me it means that there are needs that we are not aware of. When we become aware we are free to act or not on that awareness. For example, we may not be aware that many African students sit on the ground rather than a desk at school.
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An interpretation: There are few things that are really necessities in life. Being conscious of the things we call a necessitie while they have nothing to do with keeping yourself alive, means freedom. Being free of imaginary necessities.
A chair is an imaginary necessity.