intuitive explanation 1s electron behavior

The 1s electron sits way closer to the nucleus compared to others. On top of that it rotates way slower around the nucleus as well. If we average all the movement out over time we can determine what the chance is of finding the electron in a certain position. We will find that there is a chance of finding the electron inside the nucleuc, thanks to the slow rotation of this electron. This leads to extra interactions that otherwise wouldn’t happen.