"Sufficient unto the day is the evil thereof" is an aphorism which appears in the Sermon on the Mount in the Gospel of Matthew — Matthew 6:34. It also appears in the sermon at the temple in the Book of Mormon- 3 Nephi 13:34. Its meaning is the philosophy that one should live in the present, without a care for tomorrow. The same words, in Hebrew, are used to express the same thought in the Rabbinic Jewish saying dyya l'tzara b'shaata (דיה לצרה בשעתה), "the suffering of the (present) hour is enough for it". It is also similar to the Epicurean advice of writers such as Anacreon and Horace — quid sit futurum cras, fuge quaerere (avoid asking what the future will bring) — but Jesus's point was that God knew the worldly needs of men and so it was more important to seek his kingdom.I thought of this passage while reading a passage in this GetMotivated subreddit:
The human being is meant to bear the burden of 24 hours -- no more, no less. If you live in the future, you will get anxious; if you live in the past, you will get depressed. Twenty four hours is all that you have to live in. Give up all the other burdens to the universe, to god, to your cat, to whatever - but the burdens of the past are not yours. The burdens of the future aren't yours either. Let them go. The day is your material. It's what's in front of you, it's the only thing that you have the power to change or to shape or to use. It's your canvas. It's your material. So use it well.The other thoughts are also expressed rather well.