Quotations about:
    daydream

A measure of day-dreaming is a good thing, like a drug prudently used; it allays the sometimes virulent fever of the over-active mind, like a cool wind blowing through the brain to smooth the harshness of untrammelled thought; it bridges here and there the gaps, brings things into proportion and blunts the sharper angles. But too much submerges and drowns.

[Une certaine quantité de rêverie est bonne, comme un narcotique à dose discrète. Cela endort les fièvres, quelquefois dures, de l’intelligence en travail, et fait naître dans l’esprit une vapeur molle et fraîche qui corrige les contours trop âpres de la pensée pure, comble çà et là des lacunes et des intervalles, lie les ensembles et estompe les angles des idées. Mais trop de rêverie submerge et noie.]

Victor Hugo (1802-1885) French writer

Les Misérables, Part 4 “Saint Denis,” Book 2 “Eponine,” ch. 1 (4.2.1) (1862) [tr. Denny (1976)]
    (Source)

(Source (French)). Alternate translations:

A certain amount of reverie is good, like a narcotic in discreet doses. It soothes the fever, sometimes high, of the brain at work, and produces in the mind a soft and fresh vapour which corrects the too angular contours of pure thought, fills up the gaps and intervals here and there, binds them together, and blunts the sharp corners of ideas. But too much reverie submerges and drowns.
[tr. Wilbour (1862)]

A certain amount of reverie is good, like a narcotic taken in discreet doses. It lulls to sleep the at times harsh fevers of the working brain, and produces in the mind a soft and fresh vapor which corrects the too sharp outlines of pure thought, fills up gaps and spaces here and there, and rounds the angles of ideas. But excess of reverie submerges and drowns.
[tr. Wraxall (1862)]

A certain amount of dreaming is good, like a narcotic in discreet doses. It lulls to sleep the fevers of the mind at labor, which are sometimes severe, and produces in the spirit a soft and fresh vapor which corrects the over-harsh contours of pure thought, fills in gaps here and there, binds together and rounds off the angles of the ideas. But too much dreaming sinks and drowns.
[tr. Hapgood (1887)]

A certain amount of reverie is good, like a narcotic in discreet doses. It soothes the fever, occasionally high, of the brain at work, and produces in the mind a soft, fresh vapor that corrects the all too angular contours of pure thought, fills up the gaps and intervals here and there, binds them together, and dulls the sharp corners of ideas. But too much reverie submerges and drowns.
[tr. Wilbour/Fahnestock/MacAfee (1987)]

A certain amount of daydreaming does you good, like a narcotic in small doses. It sedates the sometimes severe fevers of the toiling intellect and produces in the mind a cool and gentle mist that softens the over-harsh contours of pure thought, fills in the gaps and intervals here and there, creates cohesion and smooths the sharp edges of ideas. But too much daydreaming drags you down and overwhelms you.
[tr. Donougher (2013)]