If you don't have the money already to make an investment, don't borrow it! Don't borrow it from your retirement funds, don't borrow it from the equity in your house, don't borrow it from friends or family. Why? Well, what are you going to do if the "investment opportunity" doesn't pan out the way you think it will and you end up losing all or a significant portion of the investment. Do you have the financial resources to be able to repay the loan (even if it is to yourself) if the investment goes bust, in addition to your other financial obligations?
On the other hand if you already have money set aside for investments like these, can afford to risk losing all or a major portion of it without causing yourself and your family undue hardship or stress AND know enough about the investment to consider it a safe bet, then by all means go ahead and make the investment, because that is how rewards are reaped.
Also, that last bit about KNOWING enough about the investment is really important, and there is a world of difference between KNOWING and BELIEVING. Don't just believe it because someone told you or convinced you about how good the investment opportunity is, or how it is a once in a lifetime, limited opportunity, available only to early investors kind of story! As they say "caveat emptor" or "buyer beware".