there is an asymmetry in the risk/reward ratio between being long or short in the stock market

First, there is an asymmetry in the risk/reward ratio between being long or short in the stock market. (Being long means owning a stock, being short means selling a stock one does not own.) Being long has unlimited potential on the upside but limited exposure on the downside. Being short is the reverse. The asymmetry manifests itself in the following way: losing on a long position reduces one's risk exposure while losing on a short position increases it. As a result, one can be more patient being long and wrong than being short and wrong. The asymmetry serves to discourage the short-selling of stocks.
The second step is to understand credit default swaps and to recognise that the CDS market offers a convenient way of shorting bonds. In that market the asymmetry in risk/reward works in the opposite way to stocks. Going short on bonds by buying a CDS contract carries limited risk but unlimited profit potential; by contrast, selling credit default swaps offers limited profits but practically unlimited risks.