Philosophy trains the mind. Seneca, Epistles 2.16.4-6

Philosophy teaches the mind to adapt itself to every human circumstance. Thus Seneca.

Dicet aliquis, quid mihi prodest philosophia, si fatum est? quid prodest, si deus rector est? quid prodest, si casus imperat? Nam et mutari certa non possunt et nihil praeparari potest adversus incerta, sed aut consilium meum occupavit deus decrevitque quid facerem, aut consilio meo nihil fortuna permittit.

Quidquid est ex his, Lucili, vel si omnia haec sunt, philosophandum est; sive nos inexorabili lege fata constringunt, sive arbiter deus universi cuncta disposuit, sive casus res humanas sine ordine impellit et iactat, philosophia nos tueri debet. Haec adhortabitur ut deo libenter pareamus, ut fortunae contumaciter; haec docebit ut deum sequaris, feras casum. Sed non est nunc in hanc disputationem transeundum, quid sit iuris nostri si providentia in imperio est, aut si fatorum series illigatos trahit, aut si repentina ac subita dominantur: illo nunc revertor, ut te moneam et exhorter ne patiaris impetum animi tui delabi et refrigescere. Contine illum et constitue, ut habitus animi fiat quod est impetus.

Someone shall say, "What use is philosophy to me, if fate exists? Why bother with it, if a god is our master, or again if everything submits to chance? For what is certain cannot be changed, on the one hand, and on the other, we cannot prepare anything against the uncertain. So, either a god has rendered my plan superfluous and decreed what I am to do, or fortune allows me no profit from planning."

Which of these perspectives is true? Do all things really come down to one or another of them? These are questions that must be handled with philosophy, Lucilius. Philosophy obliges us to consider whether the fates bind us by inexorable law, whether a god has set all things in their place throughout the universe, or again if chance drives and pitches human affairs, with no order at all. Philosophy will exhort us to greet gods with good cheer, and fortune with contempt. She will instruct you how to follow after the god, and to bear with the chance that befalls you. But this is not the time or place to carry our discussion on to the question of what lies in our power if providence is in command, or if an unbroken chain of fated events carries us bound, or if we are subject to the rule of sudden, unexpected accidents. So I turn back now, warning you and exhorting you not to let the ardor of your mind slip or grow cold. Extend your mind, and stablish it, so that ardor becomes natural to it.