My Latest Book

Product Details

Also available on,, and other Amazons and bookshops worldwide! 

To Think About . . .
I stopped pretending to myself that I was anything other than what I was, and began to direct all my energy into finishing the only work that mattered to me. Had I really succeeded at anything else, I might never have found the determination to succeed in the one arena I believed I truly belonged. J. K. Rowling
My Other Books

Product Details

Product Details

Product Details

Product Details

Click to order other recommended books.

Find Us on Facebook Badge

Search This Site
« Interview by Luciano Passuello | Main | Interview with Taragh B »

I'm 90 per cent sure that . . .

There’s an old saying: “It isn’t what you don’t know that hurts you — it’s what you think you know but that’s wrong!”

This article is a revised version of one that appeared in my newsletter in November 1999. It consists of a rather unusual quiz that measures exactly what you mean when you say “I am 90% sure that … ”

It may also give you some idea of what your doctor, lawyer, accountant or other professional adviser means when they tell you that they are 90% sure of something directly effecting your health and wellbeing.

The quiz questions are exactly the same as the ones I gave in 1999, so if you took the test then try it again to see how well you do now. You may find you have improved enormously — there again you may not!

Here’s the instructions. It’s important you read them carefully.

All the questions are about dates. What’s unusual is that I don’t expect you to give exact answers. In fact I have deliberately tried to pick questions to which you are extremely unlikely to know the exact answers.

What I want you to do for each question is to give a range in which you are 90% certain the answer falls. It’s entirely up to you how big that range is.

So for example if the question was “What year did John F. Kennedy enter the US Senate?” you are extremely unlikely to know the exact answer unless you are a student of political history. But from such knowledge you have of Kennedy’s life you might decide that it must have been between 1945 and 1963, so you would put down 1945-1963 as your answer. You’d be right because the correct answer is 1952!

So remember, I want you to answer each question so you are 90 per cent sure that the correct answer falls within your range. I will say that again: so you are 90 PER CENT SURE the correct answer falls within your range.

Here goes!

There are ten questions. All the answers are dates. Where not specified the date is of the first public launch/presentation. Remember you are being asked to give a range, not an exact date.

1) Chanel No. 5 perfume.

2) US Supreme Court orders the dissolution of Standard Oil Co.

3) Alexander Fleming invents penicillin.

4) Bruce Springsteen’s “Born In The USA”.

5) Mother Teresa wins the Nobel Peace Prize

6) Mississippi admitted as a state of the Union

7) Isaac Singer’s first sewing machine

8) International Society for Krishna Consciousness (the Hare Krishnas) founded

9) Tchaikovsky’s 1812 Overture

10) Louisa M. Alcott’s “Little Women”

********PAGE DOWN FOR ANSWERS**********

1) 1922 2) 1911 3) 1928 4) 1984 5) 1979
6) 1817 7) 1851 8) 1965 9) 1880 10) 1868

Remember you were asked to give a range that you were 90 PER CENT SURE the answer fell into. If you got that spot on, the date should have fallen within the range you gave for 9 out of the 10 questions. How well did you do?

Virtually everyone this test is given to gets a much lower score than 9. I’ve known some people get only one or two right. If that was your score, then when you say “I’m 90% sure” what you actually mean is “I’m 20% sure”!

The really worrying thing is that even when this type of test is given to people in subjects in which they have expert knowledge, they still tend to greatly overestimate their knowledge of the right answer.

How often do you make decisions on the basis of what you think you “know”? Realise that there is a natural human tendency to overestimate the accuracy of one’s knowledge. We think our business is doing ok, but when we check the figures they are very different from what we thought. We think we know what the trends are, but we get caught by surprise because we didn’t get the facts to back up our “knowledge”. Don’t get caught out like this — always make sure that your decisions are made on the basis of hard facts.

Once you have the facts you can then introduce other important factors such as your feelings and values, but without the facts you are building on sand.

(You won’t be surprised to hear that when I re-tested myself I got 10 out of 10. BUT, even though I’d researched all the answers myself and moreover knew exactly what to expect, I still managed to avoid getting two questions wrong by only one year — and I’d given them a 40 year and a 50 year spread respectively!)

Reader Comments

There are no comments for this journal entry. To create a new comment, use the form below.

PostPost a New Comment

Enter your information below to add a new comment.

My response is on my own website »
Author Email (optional):
Author URL (optional):
All HTML will be escaped. Hyperlinks will be created for URLs automatically.