system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: Why do intrest rates fall while average living costs increase?

I live in Germany and my interest rates plummeted over the last 10 years. I always thought, that interest rates existed to level out inflation. But I did some research and found out, that inflation rates are actually pretty stable. Meanwhile average living costs increase. How does all this fit together? 

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Sorry for bad english :)
gpt
Interest rates are controlled by central banks and are used as a tool to meet Government policies to manage the money supply and the tradeoffs between inflation and economic growth. Interest rates are however only one influcence on either of these factors and are not the core reason why costs rise or fall. 

It's not simple to Eli5  but Inflation is a result of the herd behaviour of a complex web of billions of human interactions where the price / value of millions of goods and services are constantly changing. When everyone expects prices to rise they adjust their behaviour according. In this way Central Banks have a role to guide these expectations as well as to intervene to control inflation by using interest rates to affect a change in behaviour.

What is relevant to OPs question is that almost all central banks have a Government mandated policy of targeting a low positive annual inflation rate e.g. this is 2% for the Bank of England. This is because a low positive rate has been determined to produce the best conditions for long term sustainable economic growth 

Ever since the financial crisis of 2008 intrest rates have been kept near historical lows as central banks used low rates to prop up demand and support the economy....by making money cheap it is easier to invest. It was also not seen as a good thing to raise interest rates too quickly following an economic crisis and during a period of repaying debt. It is also a matter of many debates whether they should ever return to previously higher levels. There has also not been a trigger to do so in major economies such as a case of runaway inflation or boom that would have caused Central banks to raise them quickly to act to dampen down excessive inflation.

TLDR Interest rates are a tool to control inflation..they are not it's route cause. It is possible that they may move in either direction at the time of higher/lower inflarion in response to wider economy wide issues.