How does this math work? - tchncs

There might be some simple explanation but i cannot figure it out.

You can’t just add the balances and expect it to amount to the same as the spend. Consider this: you spend 0, 0, 0, 50. Your balances are 50, 50, 50, 0. Adding up the balances you get 150. What does this mean? Absolutely nothing.
“I am your father’s brother’s nephew’s cousin’s former roommate”
“What’s that make us?”