HF band conditions are not all that good at the moment. I was on 20m (in itself an indication that conditions on the higher bands are poor) and tried to call a couple of US stations but all I got was QRZ? I heard Jarda OK1DMZ calling CQ and he was a strong signal so I replied. Back came a 599 report. It was only when I sent the station details and sent my power that I realized I had it set to 5 watts!
I've lost count of the times I've found myself accidentally operating QRP because the rig was set to 5 watts after having been WSPRing at that power level. In better conditions I've made several contacts before realizing my mistake, which just shows that QRP does not always result in having a weak signal. But when conditions are like they are at the moment, power helps!