There's no doubt that humanity has made staggering leaps in understanding the cosmos since the beginning of the 20th century. However, there is still a great deal we don't know about the universe.
To put this into context, the "normal" matter around us that makes up stars, planets, moons, asteroids, animals, tables, chairs, computers and all other everyday objects accounts for only 5% of the matter and energy in the cosmos. That means we have no real understanding of what 95% of the cosmos — sometimes called the "dark universe" — actually is.
