Most people accept the first number they are offered because they have been trained to mistake asking for something immodest. In negotiation, the employer is not doing you a favor by offering a salary; they are proposing a price for your labor, and you are entitled to propose a different one. Reason says that information — what the role pays elsewhere, what you have contributed, what the cost of replacing you is — is not aggression; it is the basis for a fair exchange.
Each step builds on the last.