First, the most important thing nobody tells beginners

You actually have two options every feeding day, not one:

The "discard then feed" method (what Nick's recipe uses) — you transfer 75 g of starter to a fresh jar, feed it, and the leftover starter is the "discard."
The "lean starter" method (what experienced bakers eventually drift toward) — you keep your starter small enough that you don't generate meaningful discard at all. More on this later.

For your first 14 days, you're locked into method #1 because that's how the recipe is written. So here's how to handle it.