Chaotic system?
Implicit in this is that there is a lot of instability in the system. A small change in sentiment can have a significant affect on the outcome, if that sentiment is relevant to the population in marginal seats. Likewise it can have a large affect on who turns out to vote on the day if it effects a group who are not usually voters (Or who become disenchanted by it).
The referendum had a significant effect on a large group of individuals who were often not particularly politically aware or even bothered by policies, but saw themselves as down-trodden English, Often "true blue" in a sense that had more to do with a kind first-half of the 20th C flag waving patriotism than Toryism. People who saw their world had changed dramatically and thought this was a way to set the clock back. May's strident "Brexit means Brexit" may well have delighted them, but the reality was always that only just over half of those who voted in the referendum were choosing to change the status quo. And the referendum non-voters, while they did not join the Remain voters, were almost by definition, not motivated supporters of a Hard Brexit either. But falling wages, social care, education funding, tuition fees, excessive wealth and executive pay rises, off-shore tax dodging, property speculation. These are things that people feel in their everyday lives.
Biting the hand that feeds IT
