Yes this is always 'interesting'. I'd personally suggest that everyone at least stuffs the following components over a 30v DC 5 amp supply (in a fume cupboard with goggles on) at least once just so you know when to wince: electrolytic capacitor reverse polarised, 1 ohm resistor, generic npn transistor (base-emitter forward biased), various LEDs, signal diodes.

you learn to double check your circuits first then :)