So, here's the first batch of postcards again:

• Design for Giants
• Be Secure Without Sacrificing Functionality
• Destructive and Non-Destructive Things Should Not Share Space
• Edge Cases Find Lesser-Used Functions Useful
• Make One Design To Rule Them All

These things will help make your software and designs more attractive to a wider swath of the population, beyond the bell curve. Those people will often be your biggest advocates and might even come to work with you on the project so they can help make it better.

And, if nothing else, maybe it will help avoid a few more experiences of hitting their head against something.