strain at a gnat make a difficulty about accepting something trivial. literary
☞ The phrase derives from Matthew 23:24, 'Ye blind guides, which strain at a gnat, and swallow a camel'. The word strain here appears to mean 'make a violent effort', but it may in fact refer to the straining of a liquid to remove unwanted particles: the image is of a person quietly accepting a difficulty or problem of significant proportions while baulking at something comparatively trivial.