What would it take to prevent highly expansionary monetary policies from being ineffective?

Have the highly expansionary monetary policies conducted in OECD countries been effective? First, effectiveness must be defined. Certainly, these policies have reduced default rates and default risk of public and private borrowers. But have they increased potential growth and the employment rate, which was one of their key objectives? Two mechanisms can severely limit the effectiveness of expansionary monetary policies from this point of view: Yield curve flattening weakens banks and may reduce the supply of bank credit and investment; The fact that the required return s on equity and capital have remained very high despite the fall in long-term interest rates may erase the effect of expansionary monetary policies on corporate investment. Conversely, if expansionary monetary policies enable higher public spending and investment, and if this increases potential growth, or if stimulating demand leads companies to become more productive and increase employment, then the effectiveness of expansionary monetary policies is enhanced. All things considered , the effect of expansionary monetary policies on potential growth (productivity gains, the employment rate) seems to be positive only when monetary policy remains expansionary while the unemployment rate is already low (i.e. when there is “overheating”).