The Liberal Democrats have been left reeling by the collapse of their vote in the 2015 election, which has left them with just eight MPs in parliament. But within just a few days of the blow, something surprising started to happen – the party was experiencing one of the largest surges of support in years.

Around 8,000 people signed up to membership in the days after the election – amounting to a new member every 39 seconds, according to the party.

Labour support is also on the rise, with 20,000 new members since election day. It may be that the new members are seeking to have a say in who the new party leaders will be now that Ed Miliband and Nick Clegg have stood down. But the increase in support in response to such a negative outcome for the parties may, in part, come down to psychology too. These new party members may well be experiencing voter regret.

People tend to think not only about how things are, but also how they might have been. Psychologists call this counterfactual thinking. When an election doesn’t go the way of our vote, we imagine how things could have turned out differently.

Counterfactual thinking leads us to experience complex emotions – and, most commonly, regret. The experience of regret is a particularly interesting psychological phenomenon. We imagine how the world might have been better and that makes us feel even worse about the current state of affairs. In other words, our reactions to events aren’t just based on reality. We let imagined worlds colour our experiences as well.

Commenting on his brother Ed’s leadership, election loss and resignation, former Labour minister David Miliband said: “There’s no point in trying to press the rewind button in life.” But, in fact, people do imagine a rewind button and pressing it can often have positive consequences.

There are likely to be lots of counterfactual thoughts about the election in part because everyone seems to agree the result was a surprise. The two main parties were tied in opinion polls, and most pundits said the next government would be a coalition. We like to speculate about what might have been when things are unexpected, because in doing so we seek to understand them: why did this happen? Why was the prediction wrong?

Voter’s regret

The very fact that people voted may lead them to feel more regret about the outcome of the election because people tend to feel more regret for outcomes they are personally involved in. Those who didn’t vote will find it easier to just walk away.

What’s more, we engage in more counterfactual thinking when things go badly than when they go well. Nick Clegg and Ed Miliband are more likely to be wondering about what they could have done differently in the election campaign than Cameron is. So if you deliberated over voting tactically, and the result was not what you hoped, you may have been preoccupied with thoughts of what would have happened if you (and others like you) had voted differently.

Who’s sorry now?EPA/Andy Rain

People might even find themselves regretting the act of voting itself. Indeed, in the heat of the moment, we tend to regret things we have done rather than things we did not do. It’s some consolation, though, to know that in the longer term, these intense regrets fade in importance compared to regrets for not acting.

The silver lining

One puzzle for psychologists is why we feel regret at all. At first glance, it seems like it just makes us feel worse about things. But this negative emotion helps us make better decisions in the future. Experiencing regret helps us to understand why things happened and what we could have done differently to avoid them. Very young children don’t experience regret, but as they get older and start to think about what might have been, they also use this experience to make better choices in the future.

However, the negative consequences of counterfactual thinking can help us understand the world and spur us in to action. Indeed, this might provide a clue to the increase in party membership after disappointing election results.

In trying to understand where the campaign went wrong, voters will imagine counterfactual worlds in which different choices were made and resulted in a more positive outcome. These counterfactual thoughts might encourage people to think about how their actions could help to bring about a better political future. And for that reason, experiencing regret and disappointment might be the beginning of a path to more political engagement in the future.

Sarah Beck receives funding from the UK Economic and Social Research Council. She has previously been funded by the British Academy and the Experimental Psychology Society.