The focusing effect is the tendency to place excessive weight on one particular aspect of an event or decision while neglecting all other factors — leading to distorted predictions about the impact on well-being.

The Weather-Happiness Study

Kahneman and Schkade asked people how happy they thought Californians were compared to Midwesterners. Both groups predicted Californians were happier because of the weather. Actual life satisfaction surveys found no significant difference. The question made weather salient; people then over-weighted it.

The Nothing Is As Important As You Think Principle

Whatever you're focusing on will loom unreasonably large in your predictions. The new car, salary raise, or house will affect your happiness less than you think — because when you're living it, dozens of other factors compete for attention.

Real-World Distortions

• Overestimating how much a raise will improve happiness
• Overestimating how much a negative event (rejection, failure) will reduce it
• Major purchase decisions that over-index on a single feature

The Fix

Deliberately list all the factors you're not currently focused on when making a prediction about future well-being.

Reference:

Wikipedia: Focusing Effect

https://en.wikipedia.org/wiki/Focusing_effect