Complex sentence: To an observer, they may appear to be affecting a blank stare into the distance, and only a sudden stimulus will startle the daydreamer out of their revhas long been derided as a lazy, non-productive pastime, daydreaming can be constructive in some contexts.
Split into simpler sentences: To an observer, they may appear to be affecting a blank stare into the distance, and only a sudden stimulus will startle the daydreamer out of their reverie. While daydreaming has long been derided as a lazy, non-productive pastime, daydreaming can be constructive in some contexts.