You mean never overestimate anybody. Or maybe, "You can never underestimate anybody."

I meant what I read somewhere long time back:

  Never underestimate the power of human stupidity.

This rings a bell right now. :-)

Last week I integrated with a service using (shudder) SOAP.

I tried the XML call with curl and couldn't get it to work. I cursed, I frothed. The reply error was some Java dump, not helpful.

It took me embarrassingly long to realize I got the HTTP header fields for SOAP from something wrong I googled -- it worked when I copied the header line from old code I wrote before... :-) :-(

My approach with Stack Overflow is to never copy-paste but always re-type by hand. This forces me to understand each line of code and its behavior (and double-check any errors). I can't recommend this enough.