Utilize your financial knowledge, give your answer or opinion to the input question or subject . Answer format is not limited.

Understanding how this interpretation of kelly criterion helps the trader
The goal of the kelly criterion strategy is to find a balance between preservation of starting capital and returns. One of extreme you could bet the entirety of your account on one trade, which would maximize your returns if you win, but leave you unable to further invest if you lose. On the other extreme, you could bet the smallest amount of capital possible over the course of several trades to increase the probability that you'll even out to 70% accuracy over time. But this method would be extremely slow.  So for your case, investing 40% each time is one way to find an optimal balance between these two extremes. Use this as a rule of thumb though, because your own situation and investing goals may differ from the goal of  optimal growth.