It is highly NOT RECOMMENDED to use brainwallets. Humans are a horrendously low source of entropy. There are multiple research papers and programs that show that brainwallets are horribly insecure and easily cracked as what you think is a strong password probably is not a strong password.
And yet if you look here:
https://blockchain.info/address/1Au4v6dZacFVsWXeKUMJd99AtyBZeqti2L1 BTC that has been there since 2012 is still there - I posted about this here:
https://bitcointalk.org/index.php?topic=885616.0It certainly isn't a simple thing to create an effective brainwallet but it also certainly isn't impossible (as I've demonstrated for four years).