To reap the benefits of compound interest (in your favor), you need to stick to a plan. You can't dump your investment portfolio after 5 years. It's these small, daily decisions that add up over time. So while the output is multiplicative, the necessary input is only linear.
If you had to put in compounding effort, the compounding output would seem far less intriguing or worthwhile. If investment returns weren't exponential, or required exponential input to receive exponential output, it'd be far less useful of a concept.
