Set a course & hold fast. Seneca, Epistles 3.23.6-8

Set a good course for your life, one that commits you to actions whose integrity you can admire, regardless of any external fortune that might attend them. Prepare yourself for storms rather than attempt to predict the weather.

Veri boni aviditas tuta est. Quod sit istud interrogas, aut unde subeat? Dicam: ex bona conscientia, ex honestis consiliis, ex rectis actionibus, ex contemptu fortuitorum, ex placido vitae et continuo tenore unam prementis viam. Nam illi qui ex aliis propositis in alia transiliunt aut ne transiliunt quidem sed casu quodam transmittuntur, quomodo habere quicquam certum mansurumve possunt suspensi et vagi? Pauci sunt qui consilio se suaque disponant: ceteri, eorum more quae fluminibus innatant, non eunt sed feruntur; ex quibus alia lenior unda detinuit ac mollius vexit, alia vehementior rapuit, alia proxima ripae cursu languescente deposuit, alia torrens impetus in mare eiecit. Ideo constituendum est quid velimus et in eo perseverandum.

What is truly good is safe to desire. You ask me what real goods are, whence they come? I will tell you: they come from a good conscience, honest counsels, right actions, contempt for accidents of fortune, and from the calm fortitude of a life dedicated consistently to a single course. As for those who leap erratically from one scheme to another, or fail to leap and find themselves dragged about by chance: how are they going to hold onto anything fixed that might remain, wavering and wandering the way they do? Few are the men who range themselves and their affairs according to plan. The rest do not so much go as find themselves carried, like swimmers floundering about in a flood. Their fate varies wildly. One finds himself lightly cradled and carried in a gentle wave, while another is violently seized. One is borne slowly to shore and laid down, while a rushing tide casts the other out into the sea. No point wasting our desire upon the weather: we must decide what we want, set a course for the berth we choose and stick to it.