cannot do without; indispensable; absolutely necessary
Expresses that something is essential or that one cannot manage without it. Often used with a noun marked by が or は.
See also: なくてはいけない
Experience is absolutely necessary for this job.
Attaches to the negative stem of a verb (ない-form minus い) to express obligation: 'must do ~'. Equivalent to なければいけません but slightly softer.
See also: なくてはいけない
Adequate sleep is indispensable for staying healthy.
I have to submit the report by tomorrow.
I must study more, right?
無くてはいけない is the plain form of 無くてはいけません, used in casual speech instead of the polite -ません ending.
Formed from the negative て-form of ない (なくて) + は (topic particle) + いけません (polite negative of 行ける, 'can go'), literally 'if it doesn't exist, it won't go', i.e., 'it is no good without it'.