LED connected in series to resistor. All is well.
This doesn't work.
Neither does this.
This would be the schematic diagram.
Why doesn't it light up? Is this the absence of a load, even though the breadboard connection has a minimal resistance?
Straightforward answer: Wire without load sucks up all the current because its resistance is approximately 0 (see Ohm's law V = RI). Points which have approx 0 resistance between them are called electrically common.
A bit more elaborate: The voltage on the wire is equal to 0. The LED leads are connected to this wire, hence no current can flow through the LED (analogous to a bird sitting on a high voltage power supply wire). Why is V = 0 in the wire? Because there is no resistance. If you measure the pressure of a flowing river without any obstacles between two points of not inmense distance between them, they are practically the same. The water can keep on flowing though, because the initial pressure from the potential difference between the mountain top and sea level (the power source) produce the current. If there's an obstacle in the way, say a small dam, water can accumulate (as well as electrons can do) on one side of the obstacle (the resistor) creating a potential difference on each side of the obstacle. Therefore a voltage builds up. Resistors can be thought of as narrowings of a pipe, but as such, the water analogy would fail, because Bernoulli's principle would come into consideration. Even though the voltage drops just like the as pressure drops in the narrowing of a pipe, in a circuit it happens before and after the resistor, not only within it. With Bernoulli, current (mass/time) is equal everywhere. That is why the water molecules are accelerated in the narrowing in order to get the same amout of mass through. In circuits it is more like closing of lanes in a road due to an accident. The road gets narrower and technically the drivers would have to accelerate in order to get the same amount of cars through in the same time interval. In reality, they slow down, producing a traffic jam, and with so a "car potential difference" is built between before and after the accident site.