Not using exposure compensation
Matrix metering does a fine job of producing balanced exposures for the majority of day-to-day photo opportunities. However, faced with an overly bright or dark subject or scene, the camera can get things wrong. Despite Matrix metering essentially applying its own exposure compensation to deliver what it determines is an optimum exposure, it may not be accurate.
Manually dialling in exposure compensation at the time of shooting is far better than trying to rescue an under- or over-exposed image later. Pushing the brightness of an image that’s very dark in Photoshop can lead to noise in shadows, while trying to eke some detail from burned-out highlights can lead to ‘digital’-looking results.
A bright, foggy scene may appear too dark if you don’t apply positive exposure compensation: the camera wants to make the fog grey rather than white