It was boomers, not bots, who won it for the Tories. For the whole election campaign we were on the lookout for what the academics call “computational propaganda”, what the platforms call “co-ordinated inauthentic behaviour” and what the media increasingly calls, rightly or wrongly, Russian bots.

But every time we found something odd, closer inspection would reveal that the best explanation was the wonderful diversity of human experience, or, more prosaically, older voters whose desire to engage in political activism outweighed their technical literacy.

We saw fake fact-checkers, invented tax bills, shitposting and search misdirection. But what we started we can stop

In the last few days of the general election campaign, for instance, we saw accusations of a misinformation campaign aimed at smearing the family of a sick four-year-old by saying they had staged a photo of him lying on a hospital floor. This gave way to the realisation that there was no real campaign, per se; just a made-up claim posted to Facebook, shared by thousands who wanted it to be true, and cut-and-pasted on to Twitter by others who didn’t bother to rewrite it in their own words.

Real people were behind the Twitter accounts that posted #nevercorbyn every five waking minutes, or that posted suspiciously similar comments underneath Boris Johnson’s Facebook messages, or that seemed to do nothing but retweet Conservative party videos. Because real people are weird.

The internet wasn’t the place for smart campaigning. The Labour party put out slick video after slick video, outspent the Tories on Snapchat and Facebook, and handed Jeremy Corbyn’s Twitter account to someone who understands memes extremely well for the entirety of election day. The Conservatives simply sat down and spent six weeks being wilfully stupid, and it worked.

In fact, one of the few changes in strategy we saw in the online election was the Conservatives doubling down on simple and stupid. The opening of the campaign was marked by a “shitposting strategy”, with the Tory party sharing low-effort, banally funny campaign messages in the clear hope that they would get as much distribution from opponents as supporters.

But, as the election went on, that approach was dropped in favour of a brutally simple one: pick three lines, whether or not they’re true, and just repeat them, for ever, on every platform, without shame or variation. Invent some Labour policies, make up a price-tag for them, and tweet it out as the cost of Labour. Make up a taxation strategy to pay for it, and tweet that out as the party’s tax bombshell. Endlessly, humourlessly, robotically come back to “get Brexit done”. There are lessons here for other political parties, but they aren’t pretty.

There are bright spots. For all the attention paid to Facebook adverts, it’s hard to conclude that, at the very least, they matter less than policies and personalities. Over the final days of the election, from 12 November to 11 December, the Liberal Democrats and Labour each spent at least £800,000 on Facebook; but the winners, the Conservatives, spent less than £550,000: you can’t buy an election on Facebook just yet. One of the fears of Facebook’s policy on political advertising is that it exports an American view of free speech – where the freedom of unlimited political spending has become a requirement to secure multimillion-dollar war chests before even thinking about a national political career. But in the UK, the total spent on Facebook adverts “about social issues, elections or politics” – everything, from everyone, since October 2018 – is less than £20m.

In fact, the most immediate lesson from the Conservative victory has been the opposite: spend on the lower end of the scale, promote simple messages of turnout and fear, and don’t overthink it. If outriders can get a bit of media coverage for breaking the rules, great, but there’s no need to court controversy from the main account.

The story may get more complicated as time goes on. Facebook’s abysmal transparency tools, while still better than those offered by any other platform, don’t even reveal basic information such as which constituencies are targeted. Google’s reveal even less: one of the more consequential online spends by the Conservatives could be two days of buying a home-page banner on YouTube, but all the company reveals is that doing so for a day costs “over £50,000” and garners “> 10m” impressions.

Overall, Google, where the Tories outspend Labour more than two to one, is perhaps the bleakest tale for the digital campaign. All the campaigns spent money on search adverts targeted at their opponents, but the Conservatives went one step further, buying ads to appear when people searched terms such as “Labour manifesto” and “register to postal vote”. I’ve lost count of the number of times we debated whether a given move was “electoral outrage” or simply “sharp tactics”.

So what’s the silver lining? That we did this to ourselves. This wasn’t foreign interference, or non-state actors running vast bot networks. In the first week of the campaign, the Guardian reported that the tactics of the Russian state in 2016 had been adopted by politicians themselves: not simply running troll farms, but campaigning through division and provocation. And that’s what we saw, with fake fact-checkers, invented tax bills, shitposting, search misdirection and more. But what we started, we can stop. We have to.

• Alex Hern is the Guardian’s UK technology editor