Look at my example numbers, and think through how you would write the setup process for that piece of software. You'd need a ton of conditionals checking all so

Look at my example numbers, and think through how you would write the setup process for that piece of software. You'd need a ton of conditionals checking all sorts of different things, woven throughout the codebase, in many different classes, etc. With a DI framework of some kind, those conditionals would likely not exist, instead you'd be able to specify all the options, and the DI framework takes over stitching them together and finding the dependencies between them.