Okay, step by step.

I have a small pot that I use pretty frequently for soup. For context, I eat homemade meals almost exclusively. I freeze them in tupperware, because I make huge pots of soup, I mean, just absolutely massive. Obviously, when a liquid is frozen, it expands. Thus, it forms a vacuum in the container. Run under hot water, it loosens a little, but it gets stuck in there sometimes.

Now, the slightly annoying part. Sometimes, the container overflows. It's hard to fill a bunch equally, without waste, and account for the "new and improved" containers that get made every two weeks so they're all different sizes and volume. Again, water expands when frozen, so the fill line is unreliable. It gets the lid stuck, but, more importantly, leaves no gap between the lip of the container and the frozen broth. I usually press on the bottom of the containers to get rid of that vacuum, but the missing gap means I'm just pressing on a block of ice.

Imagine my surprise when I realised my square containers just perfectly sat on top of the pot when turned upside down, like a lid. Now, overfilling doesn't matter. I can just press, and it drops out, without fail. I sometimes don't even need hot water. It filled my autism-riddled brain with joy to discover this!