Easy to understand if it is explained to that level of detail each time. But what if a person that believes that way to be correct comes up to you and just says the motor is pulling 30 amps, and you do not know this person believes incorrectly...???I've run into this before:
Motor is pulling 10 amps on all 3 legs. So that means that the motor is pulling 30 amps.
10+10+10=30 is completely wrong but very easy to understand