In laymen terms, 5S is associated with a housekeeping activities. In fact, the house keeping is one of ultimate objectives in the factory environment where supposedly we can work with safety and produce items with high quality and rapid delivery; just like in our house.
In our private life, first of all, we have plenty of things. I take clothing for an example. Please observe you cabinet, how many clothing do you have? How many of them are in regular use? How many of them is not in use anymore? It is not wise to buy another set of cabinet just because you could not decide which one is more important than others. Surely, it will be a joke, if you “expand” you cabinet despite the fact that your total room can only cater for such space area. From there, you should be able to understand the importance of Seiri (separation).