Try to think of someone you know, or have known in the past, about whom your initial evaluation turned out to be incomplete, misleading or inaccurate when you came to know the person better. Now try to analyse why there were differences between your initial impression and the more accurate one you built up over time. Was this because you assumed that

the person had certain attributes or qualities because he or she fell into a certain class of person that you believe normally has those attributes, or

since the person had a certain characteristic he or she automatically had other definable attributes?