All ketchup bottles are not red.

I often have problems in finding the ketchup bottle from our refrigerator. At some point I started to notice this, and eventually realized why I did not find it. It was because I was looking for something red, but the Heinz ketchup bottle isn't actually red but transparent instead. So after it has been used for a while (I have a three year old son so it doesn't last full long), it becomes mainly transparent in color. And when I start to look for the ketchup, I can't find it because I'm searching for something red.

Today I had a short discussion with my wife which wen't about like this:
Wife: Do you know where's the ketchup?
Me: The bottle isn't red, try looking for a transparent bottle.
Wife: Oh there it is.

You get the lesson already? Well I have another close experience of similar kind.

Last week I was taking part in Helsinki testing day as a test lab assistant. I was responsible for my own stand where I had created a few testing tasks for an open-source web shop. While trying to teach people hovering about some testing related lessons, I was also experimenting with the tasks. My devilish plan was that I had created tasks for testing same areas of the app but with a different story behind the task, wanting to see how it effects people.

One of the tasks was to test a product review function, out of which which I had noticed a small issue in slightly testing it. I had created two tasks:
1. a test case with execution steps for testing the function
2. a story that went: "We have received complaints from product review section. It seems same people are doing reviews on the same products many times, which seems a bit odd.. Could you please investigate what might cause this?"

The two people running the first task, didn't really find anything to report from it. The three people running the second one found multiple issues in the function, many that I hadn't, part of them pretty solid and some maybe less so. I think that this happened (yea I know that the statistical amount of testers isn't enough to make this kind of assumption but why let that get in the way of a good story) because in the second case they thought they knew that there was a specific issue in it.

So into the lesson then: If you think you know that there is a problem of certain sort, it's a lot easier to find the problem. If you are looking for red ketchup bottle, it's a lot easier to find the red ketchup bottle. But remember --- all ketchup bottles are not red.