Under no circumstances should you trust anyone to have access to your bitcoin. Do whatever it takes to accomplish that goal. Philosophically, that's one of the core reasons bitcoin is a big deal, because at no point in history has it been possible to do that until now.
If I had followed the above advice, then I wouldn't have lost a lot of money.
Given the nature of human greed, what do you think the chances are that someone who has access to >10% of a currency will simply let it sit there and do nothing with it?
Given the nature of computer security, what do you think the chances are that Coinbase is impregnable under every imaginable circumstance? What about a rogue employee? What if the founder himself steals?
Now, the question is, what's the best way to accomplish the goal of "Don't let anyone else have access to your bitcoin, ever"? There are solutions. Find one, use it. Please. Don't make my mistake.
Look, if you use bitcoins on the internet you're basically giving them away. What you do is you keep them under your mattress and ever so often you lift up your mattress and look at them and sing a sweet little song to them. They're your friends. Your secret friends.
