She was due to leave junior school and start senior school.
Her mum took her to get her new school uniform – always a big deal for young girls.
Girls want to have exactly the right clothes, to look perfect for their start among all the other girls.
Sharry’s family weren’t rich, but her mum made sure she looked smart for her first day.
But when she got to her new school, what happened wasn’t what she expected.
The first thing one of the other girls said to her was: "Oh, do you know you’re in the wrong colour?"
What Sharry and her mum hadn’t known was that the school had updated the school uniform.
It was still blue, but a completely different shade of blue.
Without missing a beat, Sharry said: "Oh, that. Yes, of course I know I’m in a different colour – I saw the other one but I chose this one because I preferred it. It’s much nicer, don’t you think?"
And the other girl stopped dead – she didn’t know what to say.
She said: "Er… er…"
Because something was happening she hadn’t considered.
All girls update their blazers as soon as the new one comes out.
It never even occurred to this girl to consider which was better.
So she had just followed the herd.
Now, suddenly, far from being superior to Sharry by having the right blazer, she realised she’d just reacted unthinkingly.
And Sharry noticed the same reaction all day.
To every girl that mentioned she had the wrong colour blazer, Sharry gave the same answer.
She chose this colour because she preferred it; didn’t they agree it was much nicer?
And every girl had the same reaction.
They didn’t know what to say because they hadn’t considered it.
Sharry immediately went from just another wimpy new girl to someone to be treated with respect.
Someone not afraid to think for herself.
And Sharry had learned one of the most important rules of marketing.
When you position yourself, you also reposition the competition.
Sharry had turned a disadvantage into an advantage.
They thought she’d be embarrassed about having the wrong blazer.
But she said she’d compared them and chosen the other one.
She immediately positioned herself as a confident individual.
Which meant she repositioned everyone else as unthinking sheep.
And, most important, Sharry watched it happening and learned.
She learned it’s all about context.
When you position yourself, you reposition everyone else.
If you are the biggest, they must be smaller.
If you are the fastest, they must be slower.
If you are the cheapest, they must be expensive.
That’s fundamental to any positioning strategy.
Sharry had learned one of the most important lessons in marketing.
So, naturally, when she left school, she took up a career in marketing.
Today, Sharry runs the marketing for one of America’s largest supermarket chains.
It has nearly 800 supermarkets.
That’s more than Asda, or Morrisons, or Aldi, or Lidl have in the UK, and it employs 72,000 people.
Sharry is in the process of positioning it and repositioning the competition.
Just the way she learned when she was 11.
Dave Trott’s book, One Plus One Equals Three, is out now