Bitcoin is not 100% secure..
You know yourself that bitcoin prices are very volatile,
may in some time you decrease the value of your money quickly.
Yes it is not 100% sure but same with other online money that you store in your different storing website accounts. Internet is very highly risky because many people now are getting more intelligent on how to hack different websites. Even your vault in a vault with a lock in your house is not safe at all. Where is the safest place now? None.