If you look at it as Currency, it is difficult for an average person to understand it because it is different.
Bitcoin, being a different kind of a digital currency, it breaks down conventional thinking in many aspects. No central regulatory body. The concept of mining. The open-ledger (blockchain), the way miners are rewarded, how transporting value is determined by its packet size and not value, the hash rate, the concept of limited supply. The 100 Million pennies in a Bitcoin, etc.
Its difficult enough for people in the money space to thoroughly understand Bitcoin (we all say we understand it, but do we really?).
For a common person, its an overkill. Its like trying to explain the concept of TCP/IP, Networking, Routing, the Internet for someone who wants to use email. Overkill.
For a newbie or a new persons who recently knew about crypto market its very difficult that they understand bitcoin because their are many ups and downs and in ICO how to invest many points which deeply seen and than take step thats why for newbie its difficult to understand bitcoin.
I agree that Bitcoin is really is difficult to understand mostly when you discovering it alone. It has ups and downs that if you're a newbie you might leave bitcoin because of this, it also has complicated background since its an open business (I think). But its easier to understand bitcoin when a friend of yours introduce it and explain it to you personally.