Joseph Mallord William Turner - Norham Castle, on the River Tweed, c.1822–3

'Not the power to remember, but its very opposite, the power to forget, is a necessary condition for our existence.'
Sholem Asch

Like many people I went through various obsessions in my childhood. Heraldry, cricket-scoring, ping-pong, curling my hair. You know the sort of thing.

At one stage I was particularly fascinated by castles.

With great intensity I read all about motte-and-bailey design; about dungeons, keeps and crenellations. I dreamt of arrow slits, portcullises and concentric curtain walls; and the hole over the gatehouse to pour burning oil on attackers.

At Primary School around that time we had been studying seafaring through the ages, and our art teacher gave us the task of drawing appropriate pictures. The class set about sketching galleys and galleons with colourful sails and complex rigging; naval officers in white breeches and brass buttons; pirates with lit fuses under their hats.

When the exercise had been completed and our efforts submitted, the teacher summoned me to the front.

‘Jim, you seem to have drawn a castle, not a ship. The assignment was all about navigation.’

‘That’s a coastal fort, Miss. It’s there to keep an eye on the boats that are coming and going through the port.’

‘Jim, I know you love castles. But sometimes you need to learn to forget.’

I read recently in The Times (15 May, ‘Brain like a Sieve?’) about a recent breakthrough made by Facebook in the field of artificial intelligence.

Their Expire-Span method has been modelled on the naturally selective memory of the human brain. First it predicts the information most pertinent to the task in hand, and then it assigns an expiration date to less relevant data. This allows machines to selectively ‘forget’ useless information on a massive scale, freeing up memory and processing power.

‘Our brains naturally make room for important knowledge by providing easy access for recollection, rather than overwhelming the brain with every detail.’

We are accustomed nowadays to think of memory loss as an impediment to everyday existence; as a creeping curse of later life. Perhaps it helps to regard its modest manifestations more positively - as a natural process that helps us achieve focus.

And sometimes we really need the soothing balm of forgetting – when a recollection is too traumatic; a relationship too damaging; a dispute too toxic.

'To be able to forget means sanity.'
Jack London, 'The Star Rover’

In the world of business too we should learn to forget - to cast off extraneous information and unnecessary detail; to free up memory and processing power; to focus more assuredly on the matter in hand.

I have been struck by the way that Pitch presentations are often confused by the enduring presence of earlier hypotheses that contribute nothing to the final argument. We become too attached to our observations to edit them out; too seduced by our own intelligence and insight. And so our redundant conjectures stick like barnacles to the reasoning, slowing its progress, limiting its limpidity.

I have also observed how previous experience can sometimes constrain innovation - because it prompts conservatism and restricts our sense of what is possible.

‘We’ve tried that before and it didn’t work.’

Occasionally we must learn to forget past enthusiasms and perspectives; to set aside the obsolete and irrelevant. Selective amnesia can be liberating.

'The advantage of a bad memory is that one enjoys several times the same good things for the first time.’
Friedrich Nietzsche

Many years after my school seafaring art project, I had a blissful holiday with friends at Kingswear Castle in Dartmouth, an artillery fort built at the end of the 15th century. It had magnificent battlements and a robust stone staircase; a ghost that came out at night and a concrete blockhouse for Thommo to sleep in. And it overlooked the estuary of the River Dart – so that we could keep an eye on the boats coming and going through the port.

'And if she asks you why, you can tell her that I told you
That I'm tired of castles in the air.
I've got a dream I want the world to share
And castle walls just lead me to despair.

Save me from all the trouble and the pain.
I know I'm weak, but I can't face that girl again.
Tell her the reasons why I can't remain.
Perhaps she'll understand if you tell it to her plain.’

Don McLean, 'Castles In The Air'

No. 331