You could move a block held between two springs by forcing the block one way or the other. Alternatively, you can subtract the tension in one of the springs.
You could lose weight by adding a hard exercise regimen to your routine. Alternatively, you can subtract the calories you consume.
You could add pressure on somebody to behave a certain way by force, nagging, harassment, pleading, and exhortion. Alternatively, you can subtract the obstacles to make the desired behaviour easier.
You could grit your teeth and preserve your focus through sheer will-power. Alternatively, you can subtract your sources of distraction.
You could become rich by adding other sources of income. Alternatively, you can be rich even with a modest income by subtracting your needs to a bare minimum.
You could cope with a disease by overpowering your symptoms with medication. Alternatively, you can subtract the factors that cause the disease.
You could stay happy by making tremendous effort to preserve and amplify your positive emotions. Alternatively, you can subtract negative emotions – the sources of your unhappiness.