If prudential regulation depends on assessments of collateral, capital adequacy and so on, and if the valuation of assets is distorted, the bulwark against the build-up of financial imbalances will be weakened. Put in simple terms, even with the necessary prudential rules, the system may not have enough built-in stabilisers to avoid financial instability.
1 The first TLTROs took place in September 2014. In September 2014, the ECB announced the launch of the  CBPP3 and the ABSPP. 2 For more details see “The transmission of the ECB’s recent non-standard monetary policy measures” ECB  Economic Bulletin, Issue 7/2015. 4/4  BIS central bankers' speeches