Error Messages Are Evil

Peter M. Brigham pmbrig at
Mon May 12 23:08:13 EDT 2014

Someone on this list (Richard Gaskin?) once observed that the difference between a tool and a product is that a tool only has to be able to be used properly, whereas a product has to be unable to be used improperly. A well-designed application should anticipate as much as possible users' likely confusion and prevent users from doing things by mistake. Error messages are part of this process -- but they should be more in the form of "in order to do x I must know y and z, please clarify…" or "did you mean a or b?" or "I'm sorry, you can't do x in this context, do you want me to…." Even better, the interface should be designed so that even these messages are encountered rarely -- consistency is a crucial part of this. The earlier Apple OSes used to do a good job on this, mostly. Later versions not so much. Windows has always done a lousy job with consistency -- I don't know how many times I've found that I can't paste into a Windows system window.

Sorry, you got me started….

-- Peter

Peter M. Brigham
pmbrig at

On May 11, 2014, at 5:24 PM, Alejandro Tejada wrote:

> Probably, the point of Mr. Donald Norman is:
> Reduce as much as possible the chance of 
> human error... (Richmond wrote about this
> key concept in a previous message: affordance)
> "A truly collaborative system would tell me the requirements
> before I did the work. If there are special ways you want 
> stuff entered, tell me before I enter it, not afterwards. 
> How many times must we endure the indignity of typing in 
> a long strong only to be told afterwards that it doesn't fit 
> the machine's whims (more accurately, doesn't fit the 
> whims of the programmer)?"
> Yes, that is the point: The program should guide the users
> and collaborate with them... effectively stopping them
> of making ineffective or potentially dangerous actions
> and guiding users in a smart way.
> This sounds really difficult to do. It's very difficult to stop
> users from doing what they want, but not impossible.
> It's possible, but... it's wise? 
> and that is another difficult question
> to answer...
> Al
> --
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