Misidentification

Skeptics, debunkers, and people who are familiar with unusual natural phenomenon may propose that most (if not all) sightings of UFOs are simply misidentification.

Potential reasons for misidentification: 

St Elmo's Fire

Sundogs

Ball, Bead, or Ribbon Lightning

Red Sprites, Blue Jets, or Elves

Gamma Ray Bursts

Birds or other animals

Glory Scattering

Swamp Gas

Other Aircraft

Holograms

Camera and glare or lens effects

Reflections

Planets, the moon, and stars (including twinkling stars and planets)

Satellites, rockets, and the International Space Station

Lighthouses

Lamps and other man-made lights

Clouds

Temperature/Weather Inversion

Weather

Unmanned drones and aerial vehicles

Foxfire bioluminescent fungus

Fires

Fire tornados

Piezoelectricity

Earthquake events

Balloon (NASA's, helium, weather, birthday)

Meteorites

Mirages

Optical illusions

Misidentified structures (like construction cranes)

Ribbon or bead lightning

Chinese lanterns or kites

Insects

Lasers

Visual cortex issues

Flares or Iridium Flares

Steam

Heat waves

Mirages

Falling space debris or satellites

Smears or dust

Pareidolia

Seizures

Bats