I don't think I agree with your definition of "robust" in this context. A bank that only writes loans and doesn't have deposits must be lending out its own assets. In that case, they don't have a reserve, because the assets they're using to back their loans aren't liabilities, and aren't subject to runs. The reserve ratio is there precisely because banks are loaning out deposits, and deposits are liabilities. If a crisis comes, there can be a run on the bank, and all of a sudden the bank is insolvent. So a bank that's only writing loans and not taking deposits (if you can call it a bank at all; it's really more of a hedge fund) is in some ways more "robust" than a traditional bank that's lending out its deposits.