In social contexts, one area to look is within the field of cognition. John Bargh’s famous experiment showed that whether we hold a cold or warm drink in our hand prior to meeting them for the first time influences our subsequent impression of them - this is called priming.

Stimuli that influence our attitudes to others do not only come from the environment. They also are processed internally. There is a vast field of experiments in social cognition (especially implicit cognition, happening in the first 200 milliseconds or less in ways we are not ‘aware’). These experiments show that unconscious evaluations and categorisations of others happen lightning quick, and influence later (conscious) attitudes we have towards them. These evaluations are made from everything from facial symmetry, height, weight, voice depth, accent, smell, age, gender and status. 

We also generalise experiences. Let’s say you once had a negative experience with a man with a beard. Now, you may tend to react in the same way to other men with beards as that original person - no matter that they’re different.

Most of our relationships are built in these entirely arbitrary considerations, which are in all likelihood adaptations from previous evolutionary environmental challenges.

:: Experiencing Physical Warmth Promotes Interpersonal Warmth

Lawrence E. Williams and John A. Bargh 2008

:: Implicit social cognition 2018

Adam Hahn, Bertram Gawronski