When did I say anything differently?Dk not if you live in the US. Live carry's the voltage, neutral is grounded. If you left them both floating and use a true ground reference on a multimeter you'll find 120 volts (or the local equivlant) on the live wire and 0 volts (maybe a few mv's) on the neutral wire. At least in the US's electrical system, high voltage AC in the US sometimes does anti-phase where the neutral wire carries an AC voltage 180 degrees out of phase, but not all, depends on how things are grounded outside and at the local power station. Depends on your country and exactly how the power is delivered. 3 phase in the US there is no neutral, just 3 AC phases. I'm not sure what is used around the world.
Because in most countries the neutral wire is grounded at the sub-station, so is effectively at 'near' zero with regards to earth (I say 'near' because of the small voltage drop across the cable, usually a volt or two AC).I was referring to a alternating current in general since the OP was asking why people say live voltages alternate but neutral is at zero.