Here's a little story from when I was younger.
So when I starting out in my individual care of a creature my parents used to let me own goldfish (I'm now into betas) and they, or my older sister, would help me set up the tank (water and all). So I would have these fish and it would be all happy and good until the cleaning happened. And I don't know why but I would always put that tablet thing that you drop into the water and bubbles to fizz out, in their temporary storage place (like a pitcher). But I would never do it for their tank, and I know you are supposed to, but I would think that the water was fine and only transfer the fish. I would never pour that picture into the tank, and they would die. This happened to me for a simple 5 tries, and it was all the same, I would lose some fish for my stupidity because 'the strong survive' and we would manage to keep them stable in their life expectancy.
Well, one day, I dun did it again with a fresh batch of goldfish, same thing happened just put tap water into the cleaned tank and transfer them via net, it wasn't until one fish died that I realized 'I'm screwing up again'. So I ran to the bathroom and under the sink, where we kept our fish supplies, and I took that packet of those tablets out and dropped three into the tank for safe measure. My tank was stable and the only thing that a goldfish could die from was their age.
This was a completely random memory after watching a cat video where a cat was playing with a fish bowl and knocked it over, causing the fish to spill on the floor.
If you would like more memory stories just comment if you want and I'll dig around and post more of it.