Difficulty means complexity of any situation. Something is said to be difficult if great amount of effort and skill is required to understand it. You face difficulty in tackling simple mathematical problems, riddles and puzzles, too. They are supposed to have varying difficulty levels. Any such problem is difficult or mind-boggling if you can't solve it in one shot and find it a hard nut to crack. Situations can be difficult if you don't get the better of them easily.
Success never comes easy and nothing succeeds like success. For those who taste success, it does not come naturally. The path of glory leads to the grave. Difficulties are a part and parcel of everyone's life. You will face difficulty in some or the other situation, invariably. Winners and losers can be distinguished on the basis of how they deal with difficulty. In this context, Winston Churchill had remarked, “A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty.”