Every American should know why we celebrate Martin Luther King, Jr. Day. Most of us don't.

Because of people like Martin Luther King, Jr., Susan B. Anthony, and other civil rights and human rights activists, we have made such major strides in bringing true equality to our world. But the fight isn't over yet.

So to honor the great Martin Luther King, Jr. and the causes we're still fighting for today, here are 15 quotes by MLK to get you thinking and motivated:

"Our lives begin to end the day we become silent about things that matter."

"I refuse to accept the view that mankind is so tragically bound to the starless midnight of racism and war that the bright daybreak of peace and brotherhood can never become a reality... I believe that unarmed truth and unconditional love will have the final word."

"Nothing in all the world is more dangerous than sincere ignorance and conscientious stupidity."

"Darkness cannot drive out darkness; only light can do that. Hate cannot drive out hate; only love can do that."

"We must develop and maintain the capacity to forgive. He who is devoid of the power to forgive is devoid of the power to love. There is some good in the worst of us and some evil in the best of us. When we discover this, we are less prone to hate our enemies."

"Injustice anywhere is a threat to justice everywhere."

"Human progress is neither automatic nor inevitable... Every step toward the goal of justice requires sacrifice, suffering, and struggle; the tireless exertions and passionate concern of dedicated individuals."

"We may have all come on different ships, but we're in the same boat now."

"There comes a time when one must take a position that is neither safe nor politic no popular, but he must take it because his conscience tells him it is right."

"Rarely do we find men who willingly engage in hard, solid thinking. There is an almost universal quest for easy answers and half-baked solutions. Nothing pains some people more than having to think."

"We must learn to live together as brothers or perish together as fools."

"The ultimate measure of a man is not where he stands in moments of comfort and convenience, but where he stands at times of challenge and controversy."

"I have decided to stick with love. Hate is too great a burden to bear."

"In the end, we will remember not the words of our enemies, but the silence of our friends."

"The time is always right to do what is right."