Milton's elegy for his friend Edward King, who drowned, shows conscious artistry rather than a spontaneous act of sorrow. A spontaneous act of sorrow would be an unthinking reaction to a death, in which a writer simply pours out the first words that come into their head. Milton, in contrast, clearly thought about and carefully crafted this response, using an elegy form that required discipline.
For example, a look at the following quote from the poem shows conscious craftsmanship:
Fame is the spur that the clear spirit doth raise
(That last infirmity of noble mind)
To scorn delights, and live laborious days;
But the fair guerdon [reward] when we hope to find,
And think to burst out into sudden blaze,
Comes the blind Fury with th'abhorréd shears,
And slits the thin-spun life.
For instance, the end rhymes "raise," "days," and "blaze," as well as "mind" and "find" almost certainly did not come to Milton spontaneously but were the result of a conscious effort to write a disciplined piece with a pleasing rhythmic pattern.
The alliteration in this passage also speaks to careful craftsmanship: the repetition of "s" sounds in "spur" and "spirit," of "l" sounds in "live laborious," and the repeated "b" sounds in "burst," "blaze," and "blind," are structured to place emphasis on those words.
Third, the allusion to the blind Fury Atropos of ancient Greek myth is a deliberate attempt to keep tying the poem back to a Greek pastoral tradition. Alliterative "s" sounds in "shears," "slits" and "spun" also suggest careful word choice.
Further, the theme of this passage highlights the hard labor of the poet, who "scorns delight" to labor for a higher reward. The emphasis on the work of the artist—and Edward King was a writer as well as Milton—shows that Milton did not compose rapidly or spontaneously. He notes that the long time it takes to craft a piece of poetry underscores how bitter it is for a poet's life to be cut off too soon.