Culture, really. Trust.<p>Where I work, Engineering owns the estimates. No ifs, buts or maybes. <i>We own estimates</i>. Product managers have unlimited ability to reprioritise, but we and we alone get to say how hard it&#x27;s going to be.<p>That said, another secret is: use story points. They are dimensionless units that are only meaningful within a single project. As soon as you give dollars or days, everybody has an opinion or an agenda.<p>But if you use points and project based on velocity, it&#x27;s hard to negotiate. Because you&#x27;re not negotiating. Those are the actual numbers. The actual historical data, staring you in the face.<p>(Edited for clarity)