... there is some evidence that wanting to observe an event will increase the probability of it happening. Combine that with a location with a high density of sightings, and the probability goes up further.
My own personal UFO sighting combined both. Coincidentally (always, right?), I had been reading one of those compiliation books of old FTs and had just read something about the study that showed that there was a high concentration of French UFO sightings along fault lines. The theory was that the piezoelectric effect was causing various forms of electromagnetic radiation. I thought, well, that explains California.... Where I was heading for my dad's wedding, which was at a bed and breakfast in the shadow of Mount Shasta. That weekend, my siblings and I heard all about how Mount Shasta and environs were known as a UFO hotspot. Given the amazing scenery, it made sense. At the rehearsal dinner in this little restaurant at the foot of the mountain, we got to watch the cloud cover and it really was strange. Driving back to the B&B, one of my brothers pointed out this weird light in the sky. There were no clouds anywhere in the sky except by the mountain, which was in the other direction. It was twilight, but there was good light except in the valleys. I couldn't really watch it, as I was the one driving, but my brothers (24 and 16) and sister (13) watched it and described it and thought out loud. The weirdest thing was that it was just this cone of light, nothing like an airplane's lights, could have been a helicopter's search light but it was way too high in the sky to be searching for something on the ground. It was really strange how it was lighting up the sky around it, as there were no clouds or anything for the illumination to show on, and there was too much ambient light. The older brother said that he thought it looked like it was moving away from the light, which didn't make sense for a plane or helicopter. I couldn't watch it for more than a brief glimpse at a time, but I did get enough to see what he meant. My guess was that it was some stupid missle interception test or whatever that the Pentagon felt was worthy of spending more money than I can fathom on that we had heard about in the radio while driving up earlier that day. I hadn't heard anything about it previous to that, but my brother assured me it had been a big topic in the news of late. We found out the next morning that that's what it had been. It ended up being an IFO, but it was a UFO to us for a good 12 hours, and that was nice.