Sure, could be just lucky. But if there are several successful small studies, and several unsuccessful large ones (no idea if this is the case here), we should probably look for a better explanation.
It does not require more explanation: publication bias means null results aren't in the literature; do enough small low quality trials and you'll find a big effect sooner or later.
Then the supposed big effect attracts attention and ultimately properly designed studies which show no effect.
It does not require more explanation: publication bias means null results aren't in the literature; do enough small low quality trials and you'll find a big effect sooner or later.
Then the supposed big effect attracts attention and ultimately properly designed studies which show no effect.