Why sell an option instead of buying one?

Every option has a buyer and a seller. The last two lessons showed you what an option is and how time decay works. This lesson answers a question that follows from both: if you're going to trade options at all, why lean toward selling them instead of buying them?

The short answer is time decay. You already know it works against option buyers and for option sellers. Structurally, that gives the seller a tailwind the buyer doesn't have, on every trade, for as long as the position stays open.

A simple way to see it. Say you sell a call option with a strike far enough above the current stock price that the option's delta is around 0.20. Very roughly, that delta is the market pricing in something like a 20% chance the option finishes in the money at expiry. Sell that option, and the market's own pricing says you start with roughly an 80% chance of it expiring worthless, a win for the seller. That's not a guarantee on any single trade, probabilities don't work that way, but it's a real statistical lean that repeats every time you do it.

What you give up by selling

Selling isn't free money, and the tradeoff is real. When you buy an option, your loss is capped at what you paid, but your gain can be large if the stock moves your way. Sell an option and it's the opposite: your gain is capped at the premium you collected, but your loss on an uncovered or wide position can be far larger than what you took in. That asymmetry is exactly why position sizing, covered in Module 3, matters more to a seller than a buyer.

Selling with defined risk

This is where credit spreads, covered in Module 4, come in. Instead of selling a single option with theoretically large risk, you sell one option and buy another further away as protection. You collect a smaller net premium, but your maximum loss becomes fixed and known before you ever place the trade. That's the version of selling this site focuses on: not uncapped risk, but defined-risk spreads where the theta tailwind is real and the downside is a number you already know.

It's not either/or

Plenty of good traders buy options, especially around events where they expect a large, fast move and want defined, limited risk on the buy side. Selling isn't the "correct" side and buying the wrong one. It's a different risk shape. This site leans toward selling defined-risk spreads because that's what a risk-first approach to NDX and SPX options tends to favour, not because buying is a mistake.

Rule of thumb. If you can't say, before you enter, exactly what your maximum loss is and you're comfortable with that number, you're not ready to sell that position, no matter how good the theta looks.

What this doesn't mean

It doesn't mean buying options is a bad strategy. Big, fast, well-timed moves can make buying the better choice for a specific setup.
It doesn't mean selling options is safe or guaranteed. A high probability of profit on paper still allows for real, sometimes large, losses.
It doesn't mean skipping position sizing. The statistical edge from theta only helps if a single bad trade can't take you out of the game.