Frustrated by the behavior of some men in their workplace, a group of women working at Nike anonymously surveyed other women colleagues a few months ago about their perceptions of sexual harassment and gender discrimination at the company. The results painted a clear picture of a workplace where women often felt marginalized, disrespected, and discriminated against. The survey reached the hands of the company’s CEO. What followed, as covered in the media, has been a serious wave of changes: Top executives at the firm resigned or are on their way out, and bias training and other remedies are being introduced.

The gesture by the Nike workers may seem dramatic, but it was the result of women being ignored by HR as they voiced their concerns. Their experience is not unique. Those working in HR departments have the responsibility to assure that people are treated fairly at work. But they may not give an employee’s complaint the attention it deserves when it is targeted to powerful executives, as a way to protect both the executives and also the company from negative media attention or even from a lawsuit. But as research tells us, an unfortunate consequence of not taking action is that more harassment is likely to take place later on as the perpetrators know they can get away with their behavior.

Stories like this one about Nike’s toxic workplace culture remind us that speaking up about injustice and being heard in an organization can create positive change. Research helps us understand why it is that people speak up in some situations and not in others.

One reason people don’t speak up is the significant risk of doing so. Challenging the status quo threatens people’s status and relationships with supervisors and coworkers, research shows. Speaking up can also result in negative performance evaluation, undesirable job assignments, or even termination. Most people are aware of these potential costs; as a result, most stay quiet about bias, injustice, and mistreatment.

Then there is the bystander effect: When a person is in trouble, others who are present often fail to intervene, whether because they assume other people will or because they think it’s not their place to act. The more costly intervening would be, the less likely we are to do so.

In one study, participants were either alone or with a passive bystander. They witnessed an incident in which a man sexually harassed a woman (in reality, both the man and the woman were actors). To vary how costly intervening was, the experimenters varied the perpetrator’s physical stature. In the low-cost condition, the perpetrator was a small man with a slight build. In the high-cost condition, the perpetrator was tall and looked fierce. When intervening would be less costly, 50% of participants helped when no other bystander was present, whereas only 5.9% of participants helped when there was another bystander. But when the cost was high, fewer participants stepped in, whether or not another bystander was present.