fake it till (someone) makes it

Translations
притворяйся, пока (кто-то) не добьется успеха
When starting a new job, sometimes you just have to fake it till you make it.
Когда начинаешь новую работу, иногда нужно просто притворяться, пока не добьешься успеха.
Definitions
A phrase meaning to act with confidence and behave as if you are successful or skilled, even if you are not yet, in order to eventually achieve success or competence.