Try taking off your glasses and then finding them again, for example, or picking up a novel in a bookshop and then struggling to locate the right place on the shelf when you come to put it back again. Wondering why you found Martin Amis's latest novel concealing the works of Jeffrey Archer on your last visit to the bookshop? Well it might have been me ... but it wasn't deliberate. Honest!
None of this is to suggest that memories are especially selective, because the mind stores all sorts of antique but apparently worthless bric-a-brac which can suddenly be transformed into vivid mental images for no particular reason. I stumbled on one of these museum pieces earlier this year when, apropos of nothing at all, or so it seemed, my mind informed me that national newspapers no longer seemed to carry those age-old advertisements featuring a forlorn face and headlines like, "Why does your memory fail you?" But perhaps I just hadn't been concentrating because, ever since I wrote on the subject in April, the ads seem to have been appearing all over the place - including on the front page of this section last week.
Reassuringly, like all national institutions, nothing much has changed with the ads: as our pictures show, they still employ the man for whom the 1960s never ended and who also finds regular work as a police photofit. And if you think he looks depressed, he clearly has good reason: not only does he forget facts and figures, but he's shamed by his English.
The similarities between the ads don't end there, because in one we're told that "a simple technique for acquiring a swift mastery of good English has just been announced", and in the other we learn that "a simple technique for acquiring a powerful memory has just been announced". Given that these techniques have been around for years, perhaps we ought to tell the copywriters that Buddy Holly's dead, Elvis Presley has just joined the army and that they should really try to remember where they're going to be when President Kennedy is shot.
If the promotions seem haphazard, however, the same cannot be said of the company behind them. R&W Heap, a small mail-order firm based in Stockport, is nearly 70 years old and runs a number of self-improvement programmes. But the main money-spinner is memory, accounting for the lion's share of sales that now total more than pounds 1m a year.
Bob Heap, the managing director, says the firm began publishing its memory courses in the early 1960s and that the pictures reproduced here could well have been taken around the same time. He couldn't confirm whether it was the antiquated nature of the ads that allowed them to steal into our minds, but they fit in perfectly with memory-improvement techniques which depend on deliberate surrealism to paint strong mental pictures.
Imagine you're on the train to work, for example, and it suddenly occurs to you that you must remember to invite an important business contact out to lunch. Haven't got pen and paper to write the idea down? Instead, form an image in your mind of the contact sitting down in a restaurant with an elephant. Chances are you won't forget it, and neither will the elephant.
I'd complained to Mr Heap that it was all right for me to write down a list of things to do, but then I'd forget to look at the list. He was so concerned that he sent me "You CAN Remember", a comprehensive 12-session course, including advice from tutors, which will cost just under pounds 200 if you still want to walk down memory lane after sending for R&W Heap's free booklet, "Adventures in Memory".
I got off to a shaky start with "You CAN Remember": I picked up session one, went off to do something else, and then couldn't for the life of me remember where I'd left it. But after this the discipline took over and I was Bunhill - Incredible Memory Man.
At the heart of the course is a number dictionary in which consonants are assigned to each numeral. For example, 't' equates to '1' because it has one downstroke, 'n' goes with '2' because it has two vertical lines, 'm' is '3' with three downstrokes, and 'r' is allocated to '4' because it is the fourth letter of the word 'four'. These letters translate into key words which the course insists should be indelibly imprinted on your memory. So 't' stands for 'tea', 'n' for 'Noah', 'm' for 'May', 'r' for 'Ray' and so on.
In the spirit of research, I put the theory to the test the other day by assigning myself three easily forgotten tasks: buy a lottery ticket, do the quick crossword and buy a bottle of wine on the way home. The weirder the association the better, advises "You CAN Remember", so I imagined celebrating a lottery win with a nice cup of tea, Noah encountering a three-letter word for boat beginning with an 'a', and sharing a bottle of red with a troupe of Morris Dancers.
And how did I get on? Well, I didn't win the lottery, I got stuck on a six-letter word for recollection starting with 'm', and the wine muddled my mind while I was trying to write a piece about memory. But who cares ... I remembered it well.
Mr Heap claims that his firm's courses have benefited countless business people, allowing them to make an impression on customers by reeling off facts and figures without recourse to their files. Want to memorise the price of one of your products? Then try '124' - that means tenner.
Disappointingly - client confidentiality and all that - Mr Heap didn't feel at liberty to identify any of these mental magicians, but I suppose you can see his point - for when readers have got total recall, who's to say that today's news is tomorrow's fish-and-chip paper?
SO THERE you are - you've trained your mind and you decide you must digest the thoughts of Rowan Gibson, a marketing consultant who recently told the European Society for Opinion and Marketing Research that "linear extrapolation ... is useless in a non-linear world".
You remember, word for word, Mr Gibson and his call for new business strategies in an uncertain age, and take the chance to introduce yourself to him at a management conference.
"Ah, you're the chap who believes 'it is vital to set up a system for rethinking the future on a never-ending basis by consulting creative people who can gather and communicate and co-ordinate information on discontinuities and who are capable of synthesising some vision out of that'. Mr Gibson, I presume?"