The ECB injected much money into the market since 2008.
The aggregate demand of an economy for goods and services cannot be increased by increasing the money supply, over a long-enough term.
Thus, what the ECB did by loosening credit was, basically, pulling the demand forward. They stole it from the future. So, they are forced to repeat these acts (injecting money, loosening credit). Otherwise the demand would decrease significantly and cause a crash of assets (bonds, stocks, real estate, etc.) leading to a high unemployment rate, defaults of government, increased incentives for accounting fraud for companies (Enron, Worldcom, Tesla?) and states (China's manipulation: banning investors from taking their money out of the market; sell orders are not being executed), etc.
I see a strong analogy to a drug lord who gives drugs (heroin) to a healthy person. This person feels strong and good because his body produces nice substances / hormones (endorphines, dopamine, etc.). The next day his body lacks these hormones. So he feels bad, worse than before having taken drugs. So he has the incentive to take the drugs again borrowing the substrates for the hormones from his body of tomorrow. This is a vicious cycle and often ends with the death of the previously healthy person.
I think the term injecting (!) money into the market has been chosen deliberately.
The healing starts when the intake of drugs is ended. This healing is very hard for the person (company, economy) for quite some time. But afterwards they can restart. The longer the substance abuse and the bigger the dose, the harder the downfall.
We all know how Escobar ended.
Let's see how the story of the ECB and Pablo Draghi will play out.
P.S. of course, today, the ECB did not hike the interest rates:
https://www.ft.com/content/a541c918-2826-36af-b12b-68e42a1af212