Physics simulations are not real life, and don't assume that simulation and reality are identical! This simulation idealizes many components. Wires and component leads have no resistance. Voltage sources are ideal - they will try and supply infinite current if you let them. Capacitors and inductors are 100% efficient. Logic gate inputs draw zero current - not too bad as an approximation for CMOS logic, but not typical of 1980s TTL for example. By all means use this simulator to help visualize circuits, but always test in reality.

Sorry to break it to you folks, but the simulator numerically approximates models of components that are also approximate. Even without allowing for any bugs it is just a rough guide to reality. This simulator may be helpful for visualization, but used the wrong way any simulator can give a false sense of security. Some people don't really grasp this important concept - I've even had one user accuse the simulator of "lying" because he (or she) didn't take account of the component idealizations and didn't understand the actual performance of the components they chose to use. It's a key leaning for all electronic engineers that they must always be fully aware of real-world component (and system) characteristics and how these differ from any particular simulator they use. If you want more precise models of real-world components then the SPICE-based simulators are much more appropriate tools than this one, but even then, you should be aware of deviations from reality. As the great analogue circuit designer Bob Pease said "When a computer tries to simulate an analog circuit, sometimes it does a good job; but when it doesn't, things get very sticky".

One consequence of the use of ideal components is that the simulator doesn't converge on a result for circuits that have no defined behaviour - for example an ideal voltage source short-circuited by an ideal wire. Another situation that can't be simulated under these assumptions is the current distribution between the conductors if two perfect conductors are connected in parallel. When using the simulator you must account for places where real electronics differs from the ideal.