If you have traveled at least once since 2006, you would know that hand luggage liquids are restricted to 3.4 oz (100 mL) per container, and need to be placed in a clear, 1 quart plastic bag. Each passenger can only carry one bag with their hand luggage (cabin bag).
However, a trend that I have noticed in my travels is that the enforcement of this differs wildly in various parts of the world. In the US, for example, liquid containers cannot exceed 100 mL or 3.4 oz, but the plastic bag/1 bag per passenger parts of the 3-1-1 rule have almost never been enforced in the last 10-15 years or so.
But in Europe, it's a different picture. The usual suspects for strict enforcement are in Britain, namely London Heathrow. In mainland Europe, it depends on the country/airport. Some do (Frankfurt and Paris, I'm looking at you), some don't (Amsterdam, Rome, Zurich, Dublin, Helsinki, etc.).
Of course, it is true that many countries, including the UK and US, have implemented new CT scanners that allow passengers to keep their liquids and electronics in their bags for screening. But is it a case that some countries simply don't see a supposed science experiment involving liquid explosives going wrong above 30,000 feet as much of a threat, whereas others do? Could it be possible that European countries are stricter due to them being more vulnerable to bad actors targeting air travel there? After all, the foiled terror plot that happened in 2006 which led to the liquids rule occurred in the UK, hence explaining their over-cautiousness.
I'd love to know your thoughts.