To live, we need salt. But if you were to eat a kilogram of salt ;it would kill you. To live in the modern world you need a car but if you don’t follow the traffic rules or if you drive while you are drunk, a car becomes a dangerous machine. Meditation is like this, it is essential for our mental health and well-being but if you practise in stupid ways it could cause problems. Some people have problems like depression, irrational fears or schizophrenia, they think meditation is an instant cure for their problem. They start meditating and sometimes their problem gets worse. If you have such a problem, you should seek professional help and after you are better then take up meditation. Other people over reach themselves, they take up meditation. and instead of going gradually, step by step, they meditate with too much energy for too long and soon they are exhausted. But perhaps most problems in meditation are caused by 'kangaroo meditation'.
Some people go to one teacher and do his meditation technique for a while, then they read something in a book and decide to try that technique, then a week later a famous meditation teacher visits town and so they decide to incorporate some of his ideas into their practise and before long they are hopelessly confused. Jumping like a kangaroo from one meditation technique to another is a mistake. But if you don’t have any severe mental problems and you take up meditation and practise sensibly it is one of the best things you can do for yourself.