To add a couple of things to the above;
. Of the list of full and part cancellations for today above, 1Y01 & 1D05 were actually due to a wiper fault on 91130 yesterday (following a bird strike, which by nature couldn't have been predicted), rather than the issue at Hitchin. The MK4 came back out of Neville Hill after repairs to start 1D05 at Leeds, and work the rest of the diagram.
. The MK4 on 1D36 (to get back to NL, partly to balance that fleet, partly for a loco exam, and in any case a need to run the last service) was a good example of the teamwork which some people are calling for above; it was picked up early by an experienced person at LNER as something which needed resolving, but with a risk regarding the route availability. A similarly experienced Controller at Network Rail arranged to amend the possession times to enable this to run via the West Riding, with the MK4; this also meant route knowledge issues with the planned diversionary route were mitigated by running via West Riding instead, given the crew displacement and the fact that not 'everyone signs everywhere' - again, this proteced the last service, which is a fundamental where at all possible.
Also not mentioned in this thread yet; after Hitchin had occurred (but at the same time that it was going on), there was a seperate incident involving multiple track circuit failures at Doncaster. This also resulted in uncertainty of route availability, and further ad-hoc amendments to the overall plan, affecting the same teams who were already snowed under.
My point here is every Controller makes hundreds of similar decisions in a shift like yesterday, both individually and as a part of the wider team(s) on duty, and some of which have to be revisions to decisions previously made and communicated, as circumstances change - the majority of these discussions and decisions might not be obvious from outside, because by nature any Controller is looking to avoid or mitigate a problem, and a problem which doesn't actually happen, sometimes isn't obvious....
Those who say that it should be better and reference political decisions made (e.g regarding unit flexibility) do have a point.... but it isn't something the teams on the day can influence too much; generally there's a set of rules which must be adhered to, and any wiggle room within those is known about and utilised.
In the meantime, spare a thought for the customers who will have been disrupted yesterday (and to some degree, this morning), and the staff, some of whom will have stayed back to help, and/or been very late getting home after a(nother) difficult shift, slept less than they'd like, and back in again today.