Is there something physiological or psychological about each horse that influences how it performs in its first up run of a campaign?

Or would first up stats be more correctly attributed to trainers? (i.e. it's their practice to start a horse "early" to complete their prep, or nudge their rating downwards, etc; or hold back a runner until it's in the right shape to contest for prizemoney straight away)

Anyone have any anecdotal stories or, better yet, stats regarding horses that maintained their 1st/2nd up characteristics despite moving between trainers who had different practices?