The following is quoted from here: https://courses.lumenlearning.com/wsu-sandbox/chapter/prejudice-and-discrimination/
When we hold a stereotype about a person, we have expectations that he or she will fulfill that stereotype. A self-fulfilling prophecy is an expectation held by a person that alters his or her behavior in a way that tends to make it true. When we hold stereotypes about a person, we tend to treat the person according to our expectations. This treatment can influence the person to act according to our stereotypic expectations, thus confirming our stereotypic beliefs. Research by Rosenthal and Jacobson (1968) found that disadvantaged students whose teachers expected them to perform well had higher grades than disadvantaged students whose teachers expected them to do poorly.
Consider this example of cause and effect in a self-fulfilling prophecy: If an employer expects an openly gay male job applicant to be incompetent, the potential employer might treat the applicant negatively during the interview by engaging in less conversation, making little eye contact, and generally behaving coldly toward the applicant (Hebl, Foster, Mannix, & Dovidio, 2002). In turn, the job applicant will perceive that the potential employer dislikes him, and he will respond by giving shorter responses to interview questions, making less eye contact, and generally disengaging from the interview. After the interview, the employer will reflect on the applicant’s behavior, which seemed cold and distant, and the employer will conclude, based on the applicant’s poor performance during the interview, that the applicant was in fact incompetent. Thus, the employer’s stereotype—gay men are incompetent and do not make good employees—is reinforced. Do you think this job applicant is likely to be hired? Treating individuals according to stereotypic beliefs can lead to prejudice and discrimination.
Another dynamic that can reinforce stereotypes is confirmation bias. When interacting with the target of our prejudice, we tend to pay attention to information that is consistent with our stereotypic expectations and ignore information that is inconsistent with our expectations. In this process, known as confirmation bias, we seek out information that supports our stereotypes and ignore information that is inconsistent with our stereotypes (Wason & Johnson-Laird, 1972). In the job interview example, the employer may not have noticed that the job applicant was friendly and engaging, and that he provided competent responses to the interview questions in the beginning of the interview. Instead, the employer focused on the job applicant’s performance in the later part of the interview, after the applicant changed his demeanor and behavior to match the interviewer’s negative treatment.
In regards to height prejudice, the self-fulfilling prophecy stems from society's treatment of shortness, such as stereotypical portrayals of short men with a complex (like in Shrek). When any short man becomes indignant over this, people label him with said complex.
As for the confirmation bias aspect, short men are the least likely to be aggressive, but people have the "angry short man" stereotype already in their heads and thus subconsciously look out for this. They could see a hundred angry men of average or tall height and not bat an eye, but the moment one short man rubs people the wrong way, it's "typical short man syndrome."
I've already written some blog posts on how people think it's the behavior itself that reinforces a stereotype, but in reality it is humanity's psychological flaws that cause this. When it comes to height, there is the added fact that humans associate size with power and authority. This is why when someone is important, we say "a man of his stature." This means short men who display assertiveness or aggression are often met with repulsion from the masses. People then subconsciously convince themselves that it's short men who have the problem, and that way any discrimination is justified.