If I understand your comment correctly, where you're getting confused is, you're reading Current Account (Assets) to mean your inventory of lemonade. What they actually mean in this case is money moved from Income to your Assets (e.g. your cash register). That's why assets went up in this example.
Of course for your lemonade business you might keep track of your lemonade as well (which I think is what you're talking about when you refer to assets). The lemonade sale would then lead to a decrease in your lemonade asset and and an increase in your expenses (cost of goods sold), so the right hand side of the equation balances.
So when selling lemonade there are actually 2 things happening:
1. Your income and your assets (your amount of cash) both increased. Income and Assets are on different sides of the =, so the equation still balances
2. Your lemonade assets decrease and you incurred the cost of that lemonade as an increase of your expenses. Those are both on the same side of the =, so the equation still balances.
