Author here. This is helpful feedback, we could have perhaps taken more time before jumping in on the Modern Bagelry example. A common misconception is that one account needs to increase while the other needs to decrease. But what we are actually showing that they can both increase or decrease in tandem, depending on the debit and credit entries in the transaction and the direction of the accounts. In the first transaction cash increases because it's a debit entry in a debit normal account (cash); and equity also increases because it's a credit entry in a credit normal account (equity).

So you basically have these two types of account, because you want all accounts to have a positive balance in general? If we would not care about certain types of accounts having negative balances, then we could say that for each transaction the sum of all account changes would always have to add up to zero. We could then still -depending on the account type- flip the sign after calculating the account balance. Am I understanding this right?

Part of the idea here is that debits = credits is a cleaner way to depict balances 'netting out to zero' than using positive or negative balances.

The main issue was that at the time the "Effect on balance by account type" figure was reversed / incorrect, and so the example was just not making sense. Reading on further and again I realized it was not the example but that figure that was wrong. I see that you fixed that now. Thanks.