I'll just start with a comparison: A composition for Piano solo contains of two staves, a stringquartet contains of four staves. My symphony contains of 37(!) staves.
The instrumentation of the orchestra for my Second Symphony (so far):
Piccolo flute, 2 flutes, 2 oboes, 2 clarinets in Bb, Bass clarinet, Soprano Sax, Alto Sax, Tenor Sax, Baritone Sax, 2 bassons, Contrabassoon, 2 Horns in F, 2 trumpets in Bb, 2 trombones, Tuba, Timpani, Percussion (Cymbals, Gongs, Snare drum, Tom-toms, Taiko drum, triangle), Tubular Bells, celesta, Piano, Harp, Strings.
As you can understand, keeping track of such a large score takes both patience and a good memory. So the process is tedious and has taken a lot of resources from me. That's why I have, on and off, been composing the first two movements for the past five months.