For a party staffer, nothing beats the start of your first general election campaign. You watch all year long as more staff are brought in and your desk space keeps getting smaller. Then, just when you thought it couldn’t get any more crowded, the campaign begins and the place is mobbed with volunteers desperate to be part of the action. Now merely having a desk qualifies you as someone of importance.

Your ego swells at the sheer magnitude of the idea that your role has some bearing on the future of a nation. You take pride in your grunt work under the brief illusion that your career choices have now been fully vindicated. No matter where the polls stand, anything is possible: you’re drunk on adrenaline, and life pulsates with hope and fear. Six weeks later, the hangover has come crashing in: you hate all politicians, you pray only for sleep, and the only question that truly burns in your soul is: when will it be over?

In the first few weeks, a typical campaign day would begin with a pre-meeting, sometime after 6am, at which we would agree on tactics ahead of the 7am daily campaign meeting. The day would end after Newsnight, and often we were still briefing weary journalists well after 11pm. In between, you gorge on Sky News and Twitter, celebrating every hit, suffering every blow, as if each mindless vox pop or inconsequential tweet represents a meaningful entry in the columns for or against ultimate victory.

If things are going well, you can literally punch a voter in the face and the world will laugh along with you

This is a gloriously uncertain election. At the last election, more than half of Labour’s voters made up their minds only in the last month, and more than a quarter in the last few days. Since then the volatility in the electorate has increased. No one will know the outcome until 12 December. However, the campaign teams at Labour and Tory HQs will be focused on a set of five questions. If mostly answered yes, these will mean a Tory majority; if mostly answered no, they will mean Labour could lead a coalition government.

The questions are: is Boris Johnson a better campaigner than Theresa May? As a true leaver, can Johnson marginalise the Brexit party? Will Midlands, northern and Welsh towns vote leave instead of Labour, regardless of the enticements in Labour’s manifesto? Without Tim Farron being weird about gay sex and otherwise forgettable, will the Liberal Democrats hold on to more of the remain support they peeled off Labour in the European elections? And finally, do the Scots really want to keep the 13 Tory MPs they surprised themselves with last time?

Party headquarters will hoover up data from private and public polling and canvass returns, especially in marginal constituencies, and will start to get a feel of how things are going within the first two weeks.

To help get a sense of where Labour should be – if Jeremy Corbyn is going to pull off another improbable surge in the polls – it is important to understand the nature of the volatility in the last election. In his essential paper looking at the data on the huge swings of votes between 2015 and 2017, Jon Mellon explains that there were really two dynamics at play.

After the 2016 referendum, voters aligned around a choice of remain v leave; after the 2017 campaign began, many of them quickly realigned back around a choice between Labour v Tory. Labour’s surge came from a swell of Labour voters who had left them after the 2015 election, and who returned as soon as it became clear that the only choice for the next prime minister was Corbyn or May.

If Labour is going to repeat the surge it had last time, even if only on a smaller scale, then we should see some change almost immediately after an election is called. Most polls are starting to show a squeeze on the smaller parties and a small bounce in the Labour vote, but we need to see a few more polls in the next week – and in particular, on Corbyn’s personal favourability ratings – to tell whether the return of Labour 2017 voters is going to be sustained and significant.

Britain is divided. That’s why we need a hung parliament again | Polly Toynbee Read more

From the perspective of a staffer, perhaps more than any single issue, that sense of whether things are going your way in the first week is what matters most in a campaign. If you are perceived to be winning, journalists start to talk about the wisdom of your strategy, and even begin to listen to what you have to say about your opponents. You begin to believe that maybe the guy running your campaign (it’s always a guy) actually is a genius. Things are simple when you’re winning: politics is just, and the public are right. If things are going well, you can literally punch a voter in the face and the world will laugh along with you.

But if you are perceived to be losing, the story is all about the pressure your campaign is under, the mistakes, and what happens when you lose. The daily campaign meetings, which should be focused on decisions, meander into complaints about the playing field being uneven and the public being misled. The ambitious MPs and special advisers start to drift off to form leadership campaigns. It is left to some unfortunate junior staffer in the sparsely attended daily campaign meeting to read out to the party chair the briefings against him (always a him) from the people who no longer come.

Losing campaigns are grim. Winning is everything. But, at least for the first glorious week, anything is possible.

• Theo Bertram is a former adviser to Tony Blair and Gordon Brown