SID EAST makes some good points. Unfortunately, ATCOs are, so far as the legal system is concerned, in a similar boat to almost any other professional. Doctors, dentists, even solicitors etc can be sued if through their negligence damage is caused.
To my mind it is not something which should be drilled into trainees as a kind of fear factor. The important thing is to learn the rules and how to apply them properly and then get on with doing what is a very enjoyable job.
At most ATC Units there are also "best practices" which are taught as part of Unit training. These practices have been found to work in most situations and by following them a lot of bother is usually saved. Of course, you have to remain flexible and open to factors which might require an alternative.