I spend an average of about 10 minutes on an electronics problem, because I sometimes make some stupid oversights. Like doing a long equation, looking for another equation to solve for a voltage output in the first and coming to a brick wall. I had to do this one particular problem which had a simple ideal op-amp. From now on I will always remember that th volage inputs to the op amps are the same and if there is a short circuit connecting a stupid input that means 0 volts, let me say that again so it will stick in my head 0 volts! Damn, I'm stupid.