Lack of Education
While all sports require a bit of education about rules, regulations and traditions, it's especially critical in air sports.
Education isn't just about the sport itself. While you need to maintain your equipment and understand how to properly participate in whichever sport you're interested in, you also need to be aware of your surroundings. If you're not educated about the terrain you'll be flying over, you may be in for a risky landing without even knowing it. If you are paragliding or hang gliding, this might mean attempting to land in a rocky area and possibly ending up breaking or spraining a leg by getting caught on a jagged stone.
Despite regulations and rules, misinformed individuals take to the sky every year; the deaths and injuries that ensue are easily preventable.