According to The National Science Foundation and UCLA psychologist Adriana Galvan, teenagers may not be the overly "moody" nutjobs that TV and movies have often said they are. Odd, I know!
"Teenagers experience stress as more stressful and if that stress is interfering with their decision making, it's really important to understand the neural mechanism that's underlying this connection between high levels of stress and poor decision-making."
Galvan also says that when teenagers see an increase in their stress levels, they're less likely to think about how their decisions will affect them in the future —on top of already being more open to risky decision-making in general.
Or, in short, parents just don't understand.