Misgendering can happen in a passing comment, in a medical record or in official policy. Schools, workplaces and government agencies that refuse to use a person's correct name and pronouns misgender them every day.
The effects are measurable. The Trevor Project's 2020 national survey looked at transgender and nonbinary youth. Those whose pronouns were respected by everyone they lived with attempted suicide at half the rate of those whose pronouns were respected by no one they lived with.
When misgendering happens by mistake, the common practice is to correct it briefly and move on. Deliberate misgendering has been treated as harassment under some state and local anti-discrimination laws. Misgendering also appears in news coverage of violence against transgender people, especially Black trans women, which can delay identification of victims and erase who they were.