One of the core principles of a Lightful interface is that no error should be unforgivable. Users should always be able to undo a mistake.
It's hardly a new concept - Jakob Nielsen included "Error prevention" in his ten usability heuristics almost twenty years ago. Yet even today, such simple, fundamental concepts are routinely ignored by web developers who care more about building "cool" things than getting the basics right.
The company that hosts my blog, Squarespace, is a usability criminal of the highest order when it comes to this. While the text editor looks slick and beautiful with its two-tone black translucent window and row of unlabeled(!) icons, it contains a usability land mine just waiting to be set off.
In the top right is a innocuous looking dropdown menu with the label "WYSIWYG." This is the method for switching one's edit mode between raw HTML and a preview mode. After typing in a few paragraphs, if you would like to edit in a different mode, and chooses to use this tool, an uncomfortably worded dialog box appears to warn you that all your unsaved changes will be lost. There are two buttons to click - "OK" will destroy your work, and "Cancel" will preserve it. Just to be perverse, the default choice is "OK," meaning an errant press of the enter key spells disaster.
For the user who dismisses dialog boxes too quickly, or fails to carefully read the difference between the effect of "OK" vs. "Cancel," it means lost sentences, paragraphs, or more. No undo is possible, the words are lost forever.
As you might imagine, this is exactly what happened to me ten minutes ago. I have lost my work, and lost trust in Squarespace's text editor. It's hardly an ideal way to feel about the central and most important feature of one's blog host. Bad form, Squarespace.