Imagine yourself in a tree, you are the nucleus. Your branches do not have any leaves yet, because you don’t have any electron. Suddenly a bird comes along, this bird is the electron. The bird moves fast, and it’s hard to see where exactly it is, but every time the bird lands on one of your branches, a leaf appears there. After a while a pattern starts to become visible in your branches, some places have a lot of leaves, some places have few. If someone outside the tree asks you where the bird (the electron) is, you can’t give them a straight answer. You can only tell to look at the density of the leaves, where the density is high, there will be a higher probability to find the bird there. Okay, then they ask you if you can tell them where the bird is on average? Looking closer at your branches full of leaves. If you squint your eyes you can see a very dense spherical surface around you. So you tell the outsider that on average the bird moves around on a sphere at a constant distance from you.