The past is vividly alive in the Old Town of Würzburg in Germany. Walking the spindly streets, I felt transported to the medieval days: I could practically see the ruddy burghers going about their business in the shadows of aged church facades.

Often when we engage with things of the past, with the material lives of our forebears, we’re in search of a sense of authenticity. Seeing the actual items that people, long dead, dealt with in their day-to-day lives seems in some way to bring them back: what they’ve left behind invigorates our historical imagination of what their lives were like. The things that populated the lives of expired generations gives us a visceral connection to them, and Würzburg amply provides the material for that sense of intimacy with the vanished past.

Or so I thought. The same day I so romantically strolled through the Old Town, I learned that it’s not old at all – younger, in fact, than me. The Allies bombed the place to annihilation, destroying 90 per cent of the city (more than Dresden). After the war, the Würzburgers rebuilt the Old Town exactly as it had been, a project not completed until the 1990s. So while it seems that you’re engaging with the world of yesteryear, in fact it’s a reproduction.

And that shattered the connection to the past. But why? Walter Benjamin called the uniqueness of a work of art its aura. An identical poster of The Scream (1893), even if arranged the same way as the original, will resonate far less if the viewer knows that Edvard Munch’s brush never touched it. Its aura is gone. So, upon learning of its recency, the aura of Würzburg’s Old Town dissolved – and I was left instead with a sense of falsity, nothing but an unsettling replica of authenticity.

As I approached my 40th birthday, I came across a chart that would – without exaggeration – alter my life’s course. Known as the U-shaped ‘happiness curve’, it plots life satisfaction across adulthood. It suggests that people are, on average, happiest in their 20s, and in old age. The bit that bothered me was the middle: according to the chart, my 40s promised to be my glummest decade.

Shortly after I saw this graph, I made some major life changes – determined to buck the averages. I took a career break, lived abroad for a year, refocused my attention on family, and decided to write a book. Generally, I think it worked: I’m about to turn 45, and now feel pretty content.

So imagine my surprise to learn recently that the chart is more debated than I assumed. While the evidence (600+ papers, apparently) supports the U-shape, its applicability to you or me, well… it depends. For example, in some countries, older age doesn’t necessarily bring greater contentment, particularly if welfare support is lacking (and in some societies, midlife is the peak of wellbeing). There may also be gender differences: the mid-40s slump could be skewed by particularly unhappy men.

This year, the entire shape of the curve has been questioned. It seems the young may be unhappier than previous generations, which is flattening out the classic smile-shape into something more like Mr Spock’s arched eyebrow. In sum, it’s more complex once you dig into the data.

However, I have no regrets about making midlife decisions based on a chart. The real power wasn’t in the curve’s accuracy, but in how it gave me permission to make positive changes. And growing older has taught me that, sometimes, life’s big choices must be made with imperfect information.