Advertising
Lookalike audience
An audience the platform builds by finding people who resemble a source audience the advertiser provided.
What makes it wrong.
The mechanism, not the warning.
A source audience below the platform's minimum produces a lookalike anyway, built on too little signal, and nothing in the reporting says the model was thin. Small sources give expensive audiences that look like general targeting with extra steps.
In detail.
The platform models the source and returns a population ranked by similarity, usually cut at a percentage of the country. A one percent lookalike is tighter and smaller, a ten percent one is broader and closer to general targeting.
Everything depends on the source. A lookalike of all visitors models visiting; a lookalike of repeat purchasers models buying twice.