So are you to my thoughts as food to life.
Or as sweet-season'd showers are to the ground;
And for the peace of you I hold such strife
As 'twixt a miser and his wealth is found.
Now proud as an enjoyer, and anon
Doubting the filching age will steal his treasure;
Now counting best to be with you alone,
Then better'd that the world may see my pleasure:
Sometime all full with feasting on your sight,
And by and by clean starved for a look;
Possessing or pursuing no delight
Save what is had, or must from you be took.
Thus do I pine and surfeit day by day,
Or gluttoning on all, or all away.
The final couplet draws its essence from the opening line, echoing the opposites of lack and “surfeit”, continuing the sense of balance. 
 Note also “day by day” is a rhythmic echo of “by and by” in line ten.
Sonnet 75