rocket

not rocket science used to indicate that something is not very difficult to understand. humorous

rise like a rocket (and fall like a stick) rise suddenly and dramatically (and subsequently fall in a similar manner).

☞ The origin of this phrase is a jibe made by Thomas Paine about Edmund Burke's oratory in a 1792 House of Commons debate on the subject of the French Revolution. Paine remarked: 'As he rose like a rocket, he fell like the stick'.