How to do an arc: four more or less casual mentions, two sort of underlined, in a two hours film: Star Lord’s dad mystery in GUARDIANS OF THE GALAXY
Adds to the film, gets you engaged and thinking, totally not in the way of what is going on, drives plot in some ways and opens out the universe. Also, mystery. Also, even though it’s dialogue, uses to the maximum the adage “show don’t tell”. Could have been done whatever the film’s budget or style and would have been as or more impactful.
How NOT to do an arc: shoehorn some bad fanfiction idea into an already threadbare and short on time season of Doctor Who: see Moffat, Steven – anything by as showrunner in DOCTOR WHO.
Gets right in the way of anything new or interesting, bores even the hardened fan, reduces loyal viewers to the position of the aunt or uncle of a disabled child who must be encouraged even when wrong, cheapens a show that can cover all time and space by going back to the same plot, same tiresome easily solved “mystery”, same characters and same female character types. Also slows down the show, get shoehorned in at the least appropriate moments and disengages the audience by breaking the unspoken contract to throw the whole cosmos at us- we know deep down it will be the same four locations in Wales and the same tired fanwank introspection, not because this is central to the show or because it can’t afford anything else but because nothing else can be thought of by the boy-king in charge.
They have made a desert of infinite potential.