I’m starting to understand why BRRRR is so valuable however I am confused on why you can’t borrow against you investment the same way in a “traditional” investment as you would the BRRRR method.

If a borrower defaults, at a certain point in time, the bank forecloses (All things being equal).

Peter,When a borrower applies for a mortgage we send out a pre-approval which is good for the loan amount not the property so it covers you as a blanket approval. 

I am not deducing the additional interest I've had to pay for privately borrowed money, extra project management fees, taxes, insurance, etc that I've had to pay due to the delay. 

Many borrowers don't expect that one.Cheers!

I've heard of hard money from lender to the institution needing the funds but not straight to the borrower.

We did our first flip on credit cards and money borrowed from friends.

I haven't used one yet, but these allow you to borrow construction costs.

Main similarity is that all 3 allow the borrower to include rehab money in to the loan.I would recommend using contractors that have earned the accreditation as a Certified 203k Contractor.

When you spread fixed costs over a larger loan amount, it becomes more cost effective and the Lender is sharing risk with the borrower (vs. an all cash deal).