Imagine your program to be a factory. And in that factory you got a team of leprechauns to get a job done. Well those leprechauns are threads. And as in real life, engaging more leprechauns will (probably) get the job done faster. Since threads and leprechauns don't require actual pay, business managers often ask; "Then why not simply add more leprechauns?". Well, when leprechauns team up they need someone to manage their business. And as the business manager knows this is often a complicated undertaking. So imagine the complexity of programming such a leprechaun manager. This is why most programs are sole proprietorships. All being said, investing in a leprechaun manager might be a wise choice (sure the business manager will agree) but do accept that one such manager can only lead so many leprechauns and that for a certain job only so many leprechauns can be engaged before they start running in each other's way.
Conclusion; threads are a lot like leprechauns, magical when balanced and managed properly.
Next up: Inversion of control
