All Fools' Day a humorous term for 1 April as a day for testing the credulity of others; recorded from the early 18th century, and probably modelled on All Saints' Day and All Souls' Day.
fools and bairns should never see half-done work the unwise and the inexperienced may judge the quality of a finished article from its rough unfinished state; saying recorded from the early 18th century.
fools ask questions that wise men cannot answer a foolish person may put a question to which there is no simple or easily given answer. The saying is recorded from the mid 17th century.
fools build houses and wise men live in them a shrewd person chooses to save themselves trouble, and benefit from the effort expended by another. The saying is recorded from the late 17th century.
fools for luck a foolish person is traditionally fortunate (the same idea is expressed in Fortune favours fools). The saying is recorded from the mid 19th century.
fools rush in where angels fear to tread a foolish person will often take a step where someone wiser will be more cautious; the saying comes from Pope's An Essay on Criticism (1711).
see also children and fools tell the truth, fool, fortune favours fools, ship of fools, young folks think old folks to be fools.