In Rudyard Kipling’s poem ‘IF’, the poet has advised the readers to keep their cool in adverse conditions in life. ‘Keep one’s head’ is an idiomatic expression to mean “to remain calm and sensible when in an awkward situation that might cause a person to panic or go out of control”.
 
Keeping our calm is important as losing the temper does not solve a problem, rather intensifies that. Keeping the head cool makes us think wisely to face those tough situations, and ultimately a solution comes out.