Could you give a specific example? Sometimes ICs require external passives with specific values (e.g. a 1uF ceramic on pin 3), but you'll never really understa

Could you give a specific example? Sometimes ICs require external passives with specific values (e.g. a 1uF ceramic on pin 3), but you'll never really understand why those values because the chip is a black box to you. Usually you have to place external components because they would be too large to design onto the die itself, particularly large things like capacitors and inductors. As such their value is whatever the manufacturer says it should be and you go along with it. Often the most magical component requirements are found in RF circuits, and then you may as well go with what the manufacturer recommends because the designers probably simulated it first. That said, I would guess you're talking about things where various combinations of components would work - e.g. a voltage divider, do you use 1R/10R or 1kR/100kR? That particular example is explained quite well [here](http://electronics.stackexchange.com/questions/28897/how-to-choose-value-of-resistor-in-voltage-divider http://electronics.stackexchange.com/questions/28897/how-to-...).