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cannot do without something; indispensable; absolutely necessary
have to do
水は生活に無くてはならないものだ。
Water is indispensable to daily life.
彼はチームに無くてはならない存在だ。
He is an indispensable member of the team.
信頼は仕事に無くてはならない要素だ。
Trust is an indispensable element in work.