I think there is no probability that your account will hacked if you only keep your private key to yourself. Be careful in entering sites that requires personal information of yours because this might become the reason to hack your account. Not all sites are trustworthy, be wise and literate about it. also, if you miss some details of your private key, you cannot ope your wallet. you can make a copy of your private key in a private document so that there is back up when you forgot it.