Many composers compose pieces like they’re writing movies in a superhero franchise: all really similar, entertaining enough, but we’re bored.
In a figurative sense, the relationship between a musical composition and a musical instrument could be likened to that of a canvas and any marks it bears. This relationship is both multifaceted and causal: for example, the textured surface of a canvas can affect the nature of the material it sets forth (cf. the pencil-on-canvas work of Agnes Martin).
The musical instrument offers the same function to a composition; the relationship between the body of the performer and their instrument defines an ecology with which the musical work necessarily interacts.
This interaction could be one of compliance – the idiomatic writing of a Paganini caprice – or subversion - the impossible glissandi employed within Xenakis’s Mikka (1971). Between these two extremes is a music that sets out to exploit the aberrant characteristics of an instrument. In the case of the baroque violin, extreme bow pressure or severe detuning (amongst other techniques) will produce unpredictable sonic responses to otherwise identical physical impetuses.