Well, I hate to say this for obvious reasons, but if the magic sugar water cured my hayfever just once, I'd try it again, and if it worked again, I'd try it again.

(This tripped my positive bias sense: only testing the outcome in the presence of an intervention doesn't establish that it's doing anything. It's wrong to try again and again after something seemed to work, one should also try not doing it and see if it stops working. Scattering anti-tiger pills around town also "works": if one does that every day, there will be no tigers in the neighborhood.)