All, I am preparing for MFE (financial engineering). I could not thin of any other forum where i could seek help for clearing my doubts on financial products.

Dear experts, is my below understanding correct?

Is the r>-1 is coming from this statement

&&&1 + r&&&

if 1+r>0, then r>-1

Extract from Stochastic Calculus for Finance 1

We introduce also an interest rate 1^{n}. One dollar invested in the money

market at time zero will yield 1 + r dollars at time one. Conversely, one dollar

borrowed from the money market at time zero will result in a debt of &&&1 + r&&&

at time one. In particular, the interest rate for borrowing is the same as the

interest rate for investing. It is almost always true that r >= 0, and this is

the case to keep in mind. However, the mathematics we develop requires only

that r > -1.

Kindly guide