Quatrain 10

چون روزی و عمر بیش و کم نتوان کرد
دل را به کم و بیش دژم نتوان کرد
کار من و تو چنانکه رای من و توستگ
از مرم به دست خیش هم نتوان کرد

Dashti, quatrain 73, p. 257

chon ruzi o omr bish o kam natvaan kard
del raa be kam o bish dozham natvaan kard
kaar-e man o to chenaanke ray-ye man o tost
az mum be dast-e khish ham natvaan kard

Since life moves by life's law and not by our will,
we should spare ourselves heartbreak
—no day can we change.
Whatever we do, what we wish it to be,
we can't mold from wax the change we would have.

And literally, with glosses in parentheses, A.J. Arberry, quatrain 149, The Rubā‘īyāt of Omar Khayyām, London, 1949: 
Since it is impossible to augment or lessens (one's) sustenance and life, it is vain (lit. impossible to make oneself miserable over the less and the more; my affairs and thine, after my opinions and thine, it is impossible for us to mould -- even (though they were) like wax in our hands.

Since life and fare no more no less shall be ,
Why let that be the cause of misery;
Your life and mine we can never remold
Like wax in the hand the way we want it to be.

Saidi, quatrain 113

Translation & Discussion of the quatrain:  1. Since our lot in life and days in life cannot be made more or less - روزی , ruzi  here is not one's sustenance but specifically one's lot in life, what is alloted.  The speaker is talking about what is alloted in life and the length of time lived. 2. Our hearts cannot get distressed/sick over "less or more" -- does this have two meanings?  First, it's not good for hearts to get "sick" worrying over less or more and second, if we accept the non-alteration of life, we then should be fortified against such distress.  3. My actions and your actions, however much are the thoughts/wishes/hopes of you and me - i.e., however much we want and hope to believe that they can be changed 4. also cannot be formed/shaped out of wax in our hands -- that is, we also cannot change or reshape our past, present, and even determine a future course of action in the way we think about these events, have an opinion of the way they should be or should have been, just as we also cannot change our lot and life - هم, ham is the key word here that ties the quatrain together. 

Metrics: For all visitors, especially the readers of Persian, a common elision occurs in natavaan, which results in natvaan (نتْوان). CvCvCVC - Consonant, short vowel, Consonant, short vowel, Consonant, Long Vowel, Consonant -- in this situation, the second short vowel will be elided, that is "struck out".

In relation to this quatrain, Connie Bobroff has called my attention to an important stanza of FitzGerald's: "Although you had not cross-referenced the FitzG and Dashti, I think it's [the stanza below] the same general idea only the one has the "Oriental" 'don't even try it, it's futile' while the other has some 'Oh, might we not just try' attitude.  What's more, they are both numbered -- by coincidence of course??! -- as 73."

Ah, Love, could thou and I with Fate conspire
To grasp this sorry Scheme of Things entire,
Would not we shatter it to bits
—and then
Re-mold it nearer to the Heart's Desire!

This stanza occurs as 73/LXXIII in the first edition and CVIII in the second.  In the third and subsequent editions, it is stanza XCIX.  The only alteration from the third edition forward is in the first line where we find "Him" in place of "Fate".

Both Heron-Allen, 145, and Arberry, 236 (Romance...) trace the source of the stanza above to the Calcutta MS, Heron-Allen cites the reference as C395, Arberry, C413.  The Persian text in Heron-Allen matches Arberry's transcription:

گر بر فلکم دست بودی چون یزدان
بر داشتمی من این فلک را ز میان
ازنو فلکی دگر چنان ساختمی
کازاده به کام دل رسیدی آسان

Heron-Allen translates:
Had I, like God, control of the heavens,
Would I not do away with the heavens altogether,
Would I no so construct another heaven from the beginning
That, being free, one might attain to the heart's desire?