Efficiency Ideas

Making mistakes is not something accidental. It is intrinsic to any processes with human involvement. Avoiding mistakes should always be a part of your project plan.

Assume Mr. Careful who has a probability of 90% to do a simple task correctly. This probability varies from person to person depends on his/her carefulness, devotion to work, technical skills, etc. Say a project involves two steps. The law of multiplication of probability works against us. According to the law of multiplication, the probability of having both steps done correctly by this person is 81% (0.9*0.9=81%. Here we assume making mistakes in each step is statistically independent.). For a project that needs three steps, there will be only 73% (0.9*0.9*0.9=72.9%) of chance the final output is correct. Please see the following tables for the probabilities of completing projects without mistakes when different number of steps are involved.

Column 1: # of steps required by a project
Column 2: Probability of completing the project without mistakes

1       80.0%
2       64.0%
3       51.2%
4       41.0%
5       32.8%
6       26.2%
7       21.0%
8       16.8%
9       13.4%
10       10.7%
11       8.6%
12       6.9%
13       5.5%
14       4.4%
15       3.5%
16       2.8%
17       2.3%
18       1.8%
19       1.4%
20       1.2%

1   90.0%
2   81.0%
3   72.9%
4   65.6%
5   59.0%
6   53.1%
7   47.8%
8   43.0%
9   38.7%
10   34.9%
11   31.4%
12   28.2%
13   25.4%
14   22.9%
15   20.6%
16   18.5%
17   16.7%
18   15.0%
19   13.5%
20   12.2%

Project done by Mr. Careless who has 80% chance of doing each step correctly.

Project done by Mr. Careful who has 90% chance of doing each step correctly.

Even for a very careful person, the chance of doing a complex project that involves many steps correctly is very slim. This is also true for a simple task that is performed repeatedly. Something will go wrong in the long run. "It is a mathematical certainty" as said by Thomas Andrews, the chief designer of Titanic, about the ship's sink after hitting an iceberg. That's why it is hard to find a driver who has never been involved in a car accident. So what are we going to do about it? The answer is double check. When the task is done, we verify the result. For example, Mr. Careful could perform the same task using an alternative approach and compare the results. If the results are the same, we are 99% sure that the result is correct. This is because the probability of that the two results are the same AND wrong is only 0.1*0.1=1%. Here the law of multiplication works in our favor. So double check is the best investment of time in that we do the task twice and the chance of making mistakes reduce to its one tenth (10% vs. 1%). A careless person who has 80% chance of doing a simple task correctly could improve the chance to 96% by double checking his work (1-0.2*0.2=96%).

Work should never be a one-shot effort simply going through the required steps. The execution of steps is easy. The hard part is to verify what we have produced is correct. It is not unusual to spend twice or more time verifying the work we have done than actually doing it.