Explain why lighting a sparkler is considered a spontaneous reaction even though it doesn't stat start spontaneously

Lighting a sparkler is considered a spontaneous reaction even though it doesn't start spontaneouslybecause it can occur by itself, or without the influence of any external forces once it is given the necessary energy needed for it to begin the reaction. 
The lighting of a sparkler is a common example of a spontaneous reaction which is often given in Science textbooks and exams around the world.