Sensory Limits - The master of trickery?

When we fail to understand what it is that we are observing, either by sight, sound, smell or mere perception based on that "sixth" sense of feeling that your being watched, how does that make your mind perceive the situation and what is the outcome? Does this explain some sasquatch / bigfoot sigthing reports that seem to be really far-fetched? And what about those who have a predisposition of knowing what they are looking for? Is that the mold or template used to make everything perceived sasquatch related?