When a person worries about his future material needs, he assumes he will still be alive in that future moment. What guarantee does he have that he'll still be alive for any length of time?
If you assume you will still be alive, then you can also assume that you'll be able to meet your basic necessities.
Suppose you saw a person looking worried and you asked him, "My friend, why are you so full of anxiety?" How would you react if he replied, "Things are all right now, but I'm worried that in 10 years I might be missing something."
Of course it's ridiculous to worry about what will be so far in the future.
Actually, just as worrying about 10 years from now is fruitless, so too is worrying about what will be in one day from now. Planning is positive. Worrying is negative.
Only the present is before you. Use it properly.
(Chayai Hamussar, vol.1, pp.68-9; Rabbi Pliskin's Gateway to Happiness, pp.155-6)