"you can invest your savings. If you ain´t got any, you ain´t gonna invest". (I admit you could argue that you can borrow but still nobody ain´t lending ya if you ain´t gonna givvet baksh).
Borrowing for investing is usually a bad decision. One must invest only money he affords to lose. The only "good" way to borrow for investing is if you have plenty of wealth, but it's already locked (properties, companies) and borrowing will provide liquidity.
Also for normal people, I'd suggest to invest
only part of the savings, not all. Some should stay for unexpected problems.
However, these are (small) details. The initial rule stands.
But this is not case now as everyone wants to take advantage and always want to be rich instantly so they invest from borrowing, or if they have savings, they invest all in. The result is, they lose everything they have and are even obligated to pay their loans so they end up living miserable. But fot those who chose to be more smart and practical, they are living their lives into profits knowing they have less to lose, more to profit.