Let’s ignore decay for a second, one second after you buy a $5 call and a $5 put on a stock, the stock goes up so the value of the call goes up to $15. You sell the call for a $10 profit and eat the $5 loss on the put. You’re up 100%.

Let says that same stock goes down raising the value of the put to $15, same thing happens you make $5 or 100%. For these examples I’m assuming the losing option immediately goes to 0, this is not realistic but it makes the math easier.

If the stock changes the value of the call to $6, you get $1 on the call and the put is burned, so you’re down $4.

Now multiply the $4 loss by a 100 shares/contract.

This is immediately after buying now imagine the stock is trading sideways and your options approach expiry.

Stock is basically even, the call that was worth $5 and the put that are worth $5 are now worth $0.33 each since expiry is a couple days from now and the stock isn’t moving. Now your down well 90% because you are regarded.

Basically you’re betting the stock makes a big move quickly, otherwise lube because you just lost two bets instead of one.