They actually have to be able to play it.

I am preparing Antonin Dvořák's Carnival Overture at the moment, and as I frequently do, I play through all the string parts and write my own bowings and fingerings.  As this is a very virtuosic piece, I am hanging around the 1ste violin part for quite a while.  Just for a laugh, I decided to see which recording I could play along with on Spotify.  I started with Concertgebouw under Chailly and was very unpleasantly surprised.  He asked the orchestra to do un-human feats of accomplishment with out of proportion (literally, as the last piu mosso was almost impossible) fast tempi.  The orchestra in 1988 must have been comprised of exclusively virtuoso strings and secondly, must have been in survival modus and severely pissed off after this recording.   Anyhow, I then switched over to Boston with Seiji Ozawa and subsequently I breathed a sigh of relief.  Everything is clear as a bell, playful and in character, and most of all, playable with room for musicality and enjoyment.  Keep that in mind, conductor's looking for a thrill and ego boost!!