Sometimes you hold a thing in your hand. You just dont realize what you are holding in the first place. It is something quite desirable to someone else, but something you really do not value. Probably because you never sought it, it just came your way.
You hang on to it initially as it was already in your hands. It did seem to stay there and you had no reason to not hold on. It was not uncomfortable much, it was quite easy to just settle.
Then, something grates. You know something is not right, but you dont know what is wrong. You are effectively left holding on to something, because you have to hold on, not because you want to, without realizing you never needed to do it in the first place. It just belonged somewhere else.
The it can be anything. A job, a relationship, a book or any habit. How difficult is it to actually let go? Quite very difficult. Some habits are quite hard to break.