Rolling snowballs
It doesn't matter how little you do as long as you do it regularly and often enough. Even the smallest things add up and can form a huge snowball when you start rolling.
Consept of marginal gains was made famous by Dave Brailsford when he was coaching british cycling team. It's the idea of trying to improve everything that can be improved. Even if it seems the improvement doesn't have any meaningful effect. Everything adds up. And when you're at the top the difference between first and the second place isn't that big anyway.
In Japan they have the consept of Kaizen. That means simply improvement or to improve. In Toyota for example they get a million improvement suggestions from their eployees. Now, just identifying the need to improve is just the first step, but when you actually start doing those improvements thats when it starts to show. By the way at Toyota they implement around 90% of those suggestions!
It takes time but even small commitment to something can make the difference. Be it exercising, investment, self improvement or a new skill. The point is not how much you do it, but how often.