another way of thinking: delta neutral

for example, you find that QQQQ options are too expensive, and QQQQ will not be that volatile through OE, you can sell Jun Call (or put) and buy some QQQQ to make it delta neutral. Your position is now short gamma, meaning any movement will cause loss to you. You are also theta short, meaning you make money from time decay.

The hard part as time goes by and QQQQ moves, your position will not be delta neutral any more. Most traders would adjust the QQQQ position to make it delta neutral again. Tricky part is where and when to rebalance.

In general, if the IV of the option you sold is higher than the realized volatility by June OE, you can make money without rebalancing.

The startegy could be the opposite way if you think IV is too low.