A smart contract is a tool for changing the world. Take a loan: I send you money, your account automatically pays it back with interest. If you can't pay, a third party covers your debts, and it's all locked in at the start. We have produced programmable money.

This is remarkable because of what we can do with programmable money. Nearly the entire financial system is built from programmable money (they won't call it that). A mortgage might be a paper contract between a person and a bank, but a million mortgages in the system are pure digital. It is just software representing a value. 

• The many things that can go wrong with a bond in the real world can't happen in the pure digital world of the blockchain. The simpler abstract systems in the blockchain universe lack the sophistication of the main financial system, but the old system can run into crises like not being able to find mortgage paperwork.
• Bitcoin and Ethereum have many implementations and if they can all smoothly work together, the whole thing works like a single machine that nobody owns.

Bitcoin enables trade. it's being used for buying coffee or making international money transfers.

Ethereum is about disintermediation - a direct relationship between two people without a middleman. It is about direct communications between people, which are capable of storing and transmitting economic value without making policies and rules and without surprising you with unexpected fees.

The concept is straightforward. Two (or more) people negotiate a business deal. There's a computer in the room to take notes. When the deal has been done, it displays the terms to the participants to fine-tune. If they agree, a smart contract is made to reflect those terms. 

When Ether reached $100, it meant that so many people believed in the world they think Ethereum will create, that it is becoming inevitable.