The network is secure, but individual addresses can be hacked when proper precautions are not taken (like storing keys electronically or choosing wallets based on non-random variables) and centralized exchanges that "store your bitcoin" for you can be hacked. Not taking these distinctions seriously and not being careful enough can totally destroy your crypto experience.

Also:
7. BTC value is extremely volatile when compared against other currencies.
8. Bitcoin transaction fees are volatile and can get quite pricey.