The Errand Runner and the Blank Check
Imagine sending a runner to that never-closing auction from Lesson 1.1 with instructions to buy something on your behalf. Everything about the outcome depends on the instruction card you hand them.
Card one reads: "Buy it immediately, whatever it costs." That's usually fine — in a crowded, liquid auction the going price is the going price. But on a chaotic morning, "whatever it costs" is a blank check, and you've pre-signed it.
Card two reads: "Buy it, but pay no more than this figure." Slower, occasionally the errand fails — but the blank check stays in your pocket.
Card three is the strange one, and thousands of investors carry it without ever reading it aloud: "If you see other people selling in a panic, sell mine too — instantly, for whatever anyone will give you." Spoken plainly, it sounds insane. Sold under its official name — a "stop-loss," a word built from stop and loss, two things everyone wants — it sounds like protection. It is the single most misunderstood instruction card in retail investing, and later in this lesson you'll watch it cost real people fortunes in a single morning.
Your brokerage is the runner. The order types are the cards. This lesson is Module 4's turn from what to own — settled across Modules 1 through 3 — to the unglamorous mechanics of actually acquiring it: what the runner does, what the errand truly costs, and which cards a long-term investor should carry, which is blessedly few.