Lakshman in Ramayan was fixed in his idea to stay with mother Sita Devi according to Lord Rama's order when The Lord went to find the golden deer.  But as soon as Marici shouted for help in Rama's voice she became agitated and asked Lakshmana to go for help. 

But Lakshmana told no harm could come for Rama at any time. Finally Sita devi used harsh words saying that Lakshman wants to enjoy after the death of Rama as he is not going to help Rama in the forest.

This was like a thunderbolt for Lakshman who never even looked at Her face but only Her lotus feet. And he decided to go out to help Rama. Then the whole story of kidnap and war begins.

Harsh words are like thunderbolt which burn one without fire.