You must grind. Seneca, Epistles 2.16.1

Seneca gives Lucilius the secret to a strong mind: work it over daily. Keep the promises you make to yourself. Stick with your goals to the end; don't always be making new ones.

Liquere hoc tibi, Lucili, scio, neminem posse beate vivere, ne tolerabiliter quidem, sine sapientiae studio, et beatam vitam perfecta sapientia effici, ceterum tolerabilem etiam inchoata. Sed hoc quod liquet firmandum et altius cotidiana meditatione figendum est: plus operis est in eo ut proposita custodias quam ut honesta proponas. Perseverandum est et assiduo studio robur addendum, donec bona mens sit quod bona voluntas est.

I know it is clear to you, Lucilius, that nobody can live happily, or even tolerably, without pursuing wisdom—for the happy life is a product of perfect wisdom, while the tolerable one comes from wisdom that has just begun to grow. Still, though it be clear, this insight must be fortified and fixed deeper in the mind by daily meditation: there is more to gain from keeping what goals you have than from proposing good ones. You must grind, adding strength to your mind by constant study, until it is as good as your will.