What is "make a mountain out of a molehill"

vb. (context idiomatic English) To treat a problem as greater than it is; to blow something out of proportion; to exaggerate the importance of something trivial

Making a mountain out of a molehill is an idiom referring to over-reactive, histrionic behaviour where a person makes too much of a minor issue. It seems to have come into existence in the 16th century.