"Man is but a bubble" is one of the adages collected by Erasmus in his Adagia. He writes:
"Man is but a bubble. The lesson of this proverb is that there is nothing so fragile, so fleeting and so empty as the life of man. A bubble is that round swollen empty thing which we watch in water as it grows and vanishes in a moment of time. Thus Marcus Terentius Varro in the preface to his book on agriculture: 'Bearing in mind', he says, 'that I must make haste; for if, as they say, man is but a bubble, much more is this true of an old man. My eightieth year reminds me to pack my baggage, before I bid farewell to life.' . . . Nor could one think of anything, in fact, which would give a better picture of the utter nothingness of this life of ours."
Robert Dodsley, Trifles (1745), page 241. I particularly like the line: "on he goes most wond'rous wise."