The first presented trait of something outshines the rest; the first opinion you hear is crucial to your overall assessment.
The more recent the information, the better we remember it.
If you have to make immediate decisions based on impressions, the primacy effect weighs heavier. If the impressions were formed a while ago, the recency effect dominates.
To combat this, keep track of impressions throughout the process. For example, jot down a score every five minutes in an interview and calculate the average afterward.