Explain · Like I'm five version
A sourdough starter in terms of a Tamagotchi
Keeping a sourdough starter alive is exactly like looking after a tiny digital pet that you have to feed with flour instead of clicking a button.
A sourdough starter is a jar of flour and water that catches wild yeast from the air to make bread rise. Just like a Tamagotchi, you cannot leave it in a drawer or forget it exists for a week. You must feed it fresh flour and water every single day to keep the yeast hungry and happy. If you ignore it, the little beastie stops bubbling, gets a bit grumpy, and eventually develops a grey layer of liquid that looks like a sad puddle of despair.
The jar is your responsibility now, and it demands your full attention while you are trying to watch your favourite cartoons. If you go on holiday, you have to find a grandparent to babysit your jar, or else it will surely wither away and die. It does not beep at you to ask for a snack, but it does grow larger and start to overflow its jar if you give it too much to eat. It is a very demanding, sticky pet that expects you to clean its glass house constantly.
Feeding your starter is a serious job that teaches you how to be a good friend to a jar of goo. Once it is bubbly and full of life, you take a little bit out to bake a loaf of bread, which is like sending your Tamagotchi off to school. You keep the rest as your main pet, always waiting for the next meal.
Where the analogy breaks downA sourdough starter will not eventually turn into a ghost and leave you if you forget to feed it for one afternoon.