When aiming to optimise your peak potential I find it helpful to imagine your ‘best’ as an Asymptote. Do you remember from back in grade 8 math the old graph curve that approaches a line but never actually touches it? Where the distance between the curve and the asymptote tends to zero as they head to infinity?
The premise here is that you can get better and better, albeit in smaller and smaller increments, essentially forever. While a beginner could easily see 100% gains in a year of training an advanced athlete might be ecstatic with a 5% gain in their personal best over the year.
So, when I hear people say “all you can do is your best” I think it’s a little mistaken (if not just a downright knee-jerk colloquial reaction). With this theory you can NEVER do your best (presupposing you can always improve) but you can continually get closer and closer to the conceptual ceiling of whatever your life’s potential is.
If your ‘Best’ really is an asymptote then you can’t expect the same returns over time as when you first started. It takes more specificity and more advanced training to elicit the further incremental improvements. But the good news is – you can get better infinitely!