So you want to call CQ, you tune around the band a bit and find what appears to be a quiet spot. You ask a couple of times if the frequency is in use and get no response, you are good to go right? Maybe not. From a pure etiquette stand point you are, but there may be a very week DX station on a nearby frequency and you just made it impossible for many people to work that station.
The solution, look on the spotting network and make sure you are 3+ kHz away from the DX stations frequency.