If I want to invest money, it is assumed that I will borrow it from someone because,
If I have money, I can invest (end of story)
If I don’t have money, but I wish to invest, I can borrow money.
I can borrow money when there is money in the bank.
There will be money in the bank only when someone deposits them (or saves).
So the money from savings from another individual will facilitate the amount required for investments.