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If you can't keep your cool, you'll lose your position.
Literal
Composure [object-を] maintain-cannot [conditional-と] you [topic-は] position [object-を] lose [thing-に] become [warning-よ].
平静を保つ is 'to maintain composure.' 地位を失う is 'to lose one's position.' ことになる expresses an inevitable consequence: 'it will end up that.' The と conditional marks this as a general truth: losing composure always leads to losing position. よ warns.