Serena Williams made a vital point about discrimination and the need to speak up.

Sitting in the passenger seat of her car, her 18-year-old nephew behind the wheel, Serena Williams had a terrifying thought.

"In the distance, I saw cop on the side of the road. I quickly checked to see if [my nephew] was obliging by the speed limit. Than I remembered that horrible video of the woman in the car when a cop shot her boyfriend. All of this went through my mind in a matter of seconds," the tennis champion wrote on Facebook.

Williams was scared, she wrote. Were she or her nephew about to become another statistic?

"I would never forgive myself if something happened to my nephew. He's so innocent. So were all 'the others.'"

Racial bias in law enforcement and disproportionate police brutality against people of color is very real. It's telling that even someone like Williams — a celebrated, successful athlete and businesswoman — was sent into a panic just from spotting a cop car.

In her Facebook post on Sept. 27, 2016, Williams opened up about these terrifying thoughts. The post has since garnered over 117,000 Likes and 20,000 shares.

"Why did I have to think about this in 2016?" Williams asked in her post. "Have we not gone through enough, opened so many doors, impacted billions of lives?"

"I had to take a look at me. What about my nephews? What if I have a son and what about my daughters? As Dr. Martin Luther King said, 'There comes a time when silence is betrayal.'"

Williams and King are right: We all need to speak up — even though (if we're being honest) staying silent can be so much easier.

Staying on the sidelines is safe, especially if you're a white person. It can be easy to brush off ignorant comments ridiculing Black Lives Matter supporters when you hear them in line at the grocery store or sitting around the dinner table.

It's easier to share your take on last night's episode of "Game of Thrones" on Facebook than it is to share an emotionally charged post about systemic racism in law enforcement.

Silence is easy. But silence costs lives.

So here's how you can speak out and spark real change when it comes to police brutality:

1. Listen. Listen to the stories of those who've been targeted by police because of the color of their skin. Listen to the (many) amazing cops who agree that change is necessary and also want solutions. Before you speak your opinion, hear their stories. Get their perspective.

2. Educate yourself. This takes some work, but knowing the facts is crucial. Let the data about racial bias sink in. And if you're white, know that it's your responsibility to understand this issue — it's not a person of color's job to enlighten you.

3. Know when to speak up (and when to shut up). These conversations can be tough, but we have to have them. When you hear loved ones saying something problematic, chime in — even if your voice is the minority opinion. And if you're white, know when to take a step back; your voice should never drown out or contradict the experiences of those who know this discrimination firsthand.

4. Get involved. The bad news is that police brutality has been disproportionately affecting communities of color for decades. The good news is that we're finally talking about it. And there are many political leaders and grassroots efforts fighting to make change when it comes to our policies and systems. Help them do it.

And just to say it, speaking out against systemic racism and demanding we do better at protecting and serving our communities of color doesn't make Williams — or you — anti-cop.

As Williams wrote in her post, "I am a total believer that not 'everyone' is bad. It is just the ones that are ignorant, afraid, uneducated, and insensitive that is affecting millions and millions of lives."

For those millions and millions of lives, we all need to take a hint from the tennis champ: "I won't be silent."