This is generally a Steven Moffat thing and the most annoying example to date is The Name of the Doctor. Because what the hell happened next?! Not only had Clara fainted (for some bizarre reason) but, more importantly, the show had just dropped the almighty bombshell that there's always been a whole other incarnation of the Doctor that nobody has ever known about. Even the Doctor himself had suppressed the memory of this incarnation's very existence so it was a pretty big deal when John Hurt stepped out of the shadows in all his guilt ridden, war torn glory. And just in time for the 50th anniversary special, too. Apparently, though, Steven Moffat assumed that, just because the series would then be off air for 6 months, everybody would've forgotten about it by the time it eventually returned. As such, he clearly didn't feel the need to resolve all of our unanswered questions, such as how the hell they even got out of the Doctor's time stream in the first place. At the start of the next episode, The Day of the Doctor, Clara was working as an English teacher (when did that happen?) and rode a motorbike (when did that happen?) but there was no allusion - like, at all - to the fact that she had just literally sacrificed her own life in order in order to save every incarnation of the Doctor throughout his entire history. A 'thanks' would've been nice, Doctor. Besides, why weren't the Doctor and Clara travelling together at this point? And how long had they even been apart? Unfortunately the TARDIS was conveniently commandeered by a UNIT helicopter and dropped off in Trafalgar Square before any of these unresolved threads could be resolved, but that was OK, apparently, because they gave us a kick ass opening sequence instead. Who needs narrative progression when the Doctor's dangling upside down out of the TARDIS over the skies of London? And what about the final moments of The Pandorica Opens back in Series 5? It was arguably one of the most Earth shattering cliffhangers in Doctor Who history, what with Rory killing Amy, the Doctor finding himself imprisoned inside the Pandorica, River becoming trapped in an exploding TARDIS and, you know, the entire universe being obliterated. And the start of the next episode? Oh, the universe was back, the Doctor was freed (in a plot twist that still to this day doesn't make a whole lot of timey-wimey sense...) and Amy was alive again. Sorted. Seriously. The purpose of a cliffhanger is to leave us on tenterhooks, not to keep us guessing until the next episode and then completely ignore/rewrite it all from even happening. The Classic Series ended an episode with the Seventh Doctor literally hanging off a cliff once, though, so at least things haven't got that bad... yet.
Dan Butler is the Doctor Who Editor at WhatCulture.com. When he isn't writing his own articles or editing other people's, he can be found trawling the internet for gifs of Steven Moffat laughing. Contact him via dan.butler@whatculture.co.uk.