Laudator Temporis Acti

Brian Newbould, Schubert: The Music and the Man (Berkeley: University of California Press, 1999), p. 45:

Composing a song is a reactive task, composing an instrumental piece a proactive one. In that sense the instrumental project taxes creativity the more, whether it's an undertaking large or small. A necessary part of what a composer has to do is impose a limitation on himself. The possibilities facing a musical creator are immense, until the first notes are penned. Thereafter the range of options narrows, for in the succession of one thought by another, coherent continuity is demanded. Composers welcome the narrowing of options, the proliferation of limitations, which makes their task more manageable. The hardest part of a piece, accordingly, is the beginning, because there are as yet no limitations. Limitations are created by the context set up in the opening bars. However, the adoption of a verbal text creates a context before a note of music is written down or conceived. The range of options is limited at the outset by the need to relate musical invention to a verbal fait accompli.

Cf. William Wordsworth:

Nuns fret not at their convent's narrow room;
And hermits are contented with their cells;
And students with their pensive citadels;
Maids at the wheel, the weaver at his loom,
Sit blithe and happy; bees that soar for bloom,
High as the highest Peak of Furness-fells,
Will murmur by the hour in foxglove bells:
In truth the prison, into which we doom
Ourselves, no prison is: and hence for me,
In sundry moods, 'twas pastime to be bound
Within the Sonnet's scanty plot of ground;
Pleased if some Souls (for such there needs must be)
Who have felt the weight of too much liberty,
Should find brief solace there, as I have found.