Servus Hinterbänkler,
der gute alte Seneca hat in seinem 98. Brief an Lucilius Interessantes über Zukunftsangst zu sagen:
Sive alios observare volueris (liberius enim inter aliena iudicium est), sive te ipsum favore seposito—et senties hoc et confiteberis, nihil ex his optabilibus et caris utile esse, nisi te contra levitatem casus rerumque casum sequentium instruxeris, nisi illud frequenter et sine querella inter singula damna dixeris: “dis aliter visum est.” 
Immo mehercules ut carmen fortius ac iustius petam, quo animum tuum magis fulcias, hoc dicito, quotiens aliquid aliter quam cogitabas evenerit: “di melius.” 
Sic composito nihil accidet. Sic autem conponetur, si, quid humanarum rerum varietas possit, cogitaverit, antequam senserit, si et liberos et coniugem et patrimonium sic habuerit tamquam non utique semper habiturus et tamquam non futurus ob hoc miserior, si habere desierit. 6. Calamitosus est animus futuri anxius et ante miserias miser, qui sollicitus est, ut ea, quibus delectatur, ad extremum usque permaneant. Nullo enim tempore conquiescet et expectatione venturi praesentia, quibus frui poterat, amittet. 
In aequo est autem amissae rei <dolor> et timor amittendae. 7. Nec ideo praecipio tibi neglegentiam. Tu vero metuenda declina; quidquid consilio prospici potest prospice;
quodcumque laesurum est multo ante quam accidat speculare et averte. In hoc ipsum tibi plurimum conferet fiducia et ad tolerandum omne obfirmata mens.
Potest fortunam cavere qui potest ferre; certe in tranquillo non tumultuatur. Nihil est nec miserius nec stultius quam praetimere: quae ista dementia est malum suum antecedere?
For whether you prefer to observe other men (and it is easier to make up one’s mind when judging the affairs of others), or whether you observe yourself, with all prejudice laid aside, you will perceive and acknowledge that there is no utility in all these desirable and beloved things, unless you equip yourself in opposition to the fickleness of chance and its consequences, and unless you repeat to yourself often and uncomplainingly, at every mishap, the words: “Heaven decreed it otherwise!” Nay rather, to adopt a phrase which is braver and nearer the truth—one on which you may more safely prop your spirit—say to yourself, whenever things turn out contrary to your expectation: “Heaven decreed better!”
If you are thus poised, nothing will affect you; and a man will be thus poised if he reflects on the possible ups and downs in human affairs before he feels their force, and if he comes to regard children, or wife, or property, with the idea that he will not necessarily possess them always and that he will not be any more wretched just because he ceases to possess them. 6. It is tragic for the soul to be apprehensive of the future and wretched in anticipation of wretchedness, consumed with an anxious desire that the objects which give pleasure may remain in its possession to the very end. For such a soul will never be at rest; in waiting for the future it will lose the present blessings which it might enjoy. And there is no difference between grief for something lost and the fear of losing it.
7. But I do not for this reason advise you to be indifferent. Rather do turn aside from whatever may cause fear. Be sure to foresee whatever can be foreseen by planning. Observe and avoid, long before it happens, anything that is likely to do you harm. To effect this your best assistance will be a spirit of confidence and a mind strongly resolved to endure all things. He who can bear Fortune, can also beware of Fortune. At any rate, there is no dashing of billows when the sea is calm. And there is nothing more wretched or foolish than premature fear. What madness it is to anticipate one's troubles!
Mit freundlichen Grüssen
Roland
https://www.loebclassics.com/view/seneca_younger-epistles/1917/pb_LCL077.121.xml
https://en.wikisource.org/wiki/Moral_letters_to_Lucilius/Letter_98
http://www.thelatinlibrary.com/sen/seneca.ep16.shtml