If something doesn't make sense, you're not seeing something.

Oh my goodness! I keep telling myself this very thing; then I run into a challenge, forget the lesson, beat myself up for days, and then have an epiphany of relearning the lessons and finally get down to solving the challenge.

Build a minimal testcase.

Start adding things to the minimal testcase until things break.

Verify what breaks.

Ah yes! This is the very foundation for how we try to be careful about building up our test suites. Start simple, add complexity little-by-little, till it 'breaks'. The more we follow this, the better our testing and the less the cost and time. Overly complex tests with no particular problem in mind is what our management wants; but it proves repeatedly to be excessively time consuming and costly. But here's the rub (as they...whoever 'they' are...say): Why is it so hard to figure out what the 'next thing to add to try to make it break' should be?

Most people are so quick to say "Oh, I saw it once - that must be the problem!" and I'm just as bad as anyone. That time taken to truly verify the breaking piece was critical because it gave me another lead.

I've spent many a long night troubleshooting this tester tendancy instead of troubleshooting what we should be troubleshooting...the actual system problem.

The OP's wisdom is a nice summary that I, for one, find most satisfying.

Thanks, dragonchild.