Do you mean asteroids from space? Well it is very rare. Some asteroids are very big almost like planets and others are small. The small ones are unlikely to cause too much harm if they hit earth. Meteors which are also small often fall to the earth with little effect, except on the landing site. Because of all the space exploration work being done there is usually information on when and where an asteroid or meteor will fall.
Did you know: One time in history, about 65 million years ago, a huge asteroid hit earth changing it’s climate and wiped out a lot of animal and plant life. It is thought to have caused the extinction of dinosaurs.