One that desires to excel should endeavour in those things that are in themselves most excellent.

Ambition is only as good as its object. Enormous effort spent on something trivial still produces a trivial result, and the intensity of the striving does nothing to upgrade what is being striven for. Choosing the field is therefore a bigger decision than choosing how hard to work in it, and it usually gets a fraction of the thought.

Look at where the bulk of your energy currently goes and ask whether you would defend that as worth a decade. If not, the fix is not more discipline but a better target.