This final phrase is at the heart of the whole soliloquy:
Life's but a walking shadow, a poor player,
That struts and frets his hour upon the stage,
And then is heard no more.
'Is but' is an old way of saying 'is nothing but' or 'is no more than'.
It's an efficient phrase, very compressed (and guess what: da DUM—'Life's BUT.')
This phrase is at the heart of the soliloquy because it's the construction that communicates Macbeth's essential disappointment: 'When I thought I was winning, it turns out life is but...(a walking shadow, a poor player etc).'
So of all the distinctive Shakespearean phrases, this one is essential—we'll have to use it in our variation.
But exactly what you are disappointed in depends on the theme you've been developing, and what kind of nouns you've been thinking about:
Drive-thru: Work's but a trail of cars, work's but a speakerbox, work's but an endless parade, work's but a broken order, but series of nuggets, but a squawking speaker, but a smudge of grease, but a mad customer, but a cranky lady, but a long line of orders, but an endless line-up
Everything falls apart: Life’s but a falling house, life’s but a pounding wave, life’s but an endless stream, life’s but a broken contract, life’s but a subscription offer, but a bag of rags, but a catalogue display, but a rental order, but a rental contract, but a losing battle, but a tired rower, but a broken rower
To do this next activity, try boiling your theme down to one word: life, work, school, friends, family, love, dogs, pens, games, hair, whatever.
Then combine it with another noun and see what you get.
