How one aspect of something can easily cloud our overall opinion.
The Halo Effect is a well known cognitive bias.
It occurs when we judge someone, something or someplace as being wholly positive based on a single, favourable aspect.
For example, physically attractive people are perceived to be smarter, funnier and more likeable than less attractive people.
When it applies to food it’s called the Health Halo Effect.
This happens when we overestimate the health benefits of a product based on our perception of how healthy we think it is. This effect works for companies that claim to be healthy like Subway.
People tend to underestimate how calorific Subway food is, relative to a chain like McDonald’s. This in turn leads to them making higher-calorie purchases from these establishments.
The Horn Effect is the opposite.
It occurs when we let the overall appraisal of something be based on one negative trait.
For example, physically unattractive people are perceived to be less trustworthy even though there is no connection between morality and physical appearance.