I think the hardest thing is to live your own life rather than the one everyone else has planned for you. Everyone wants to tell you what you should do, what you should believe, what you should value, who you should love, where you should live, what you should drive and even how and what you should eat. They are all well meaning and sometimes you should follow their sage advice but you have to live your own life rather than theirs.
I am torn between two answers, as I am not sure which is the harder:
(a) the diamond in an engagement ring; or
(b) getting it back again after you have changed your mind.
The hardest thing in life is finding yourself! Or overcoming yourself!