As you get better at a particular routine your body will adjust as well. The same routine gets easier and easier as your muscles adapt. This is called the ‘training effect’, when your body changes according to the load you place on it. You need to progress or you will become bored…known as reaching a ‘plateau’. To avoid this, you should develop several workout routines or work out plans with different levels of intensity.
If you are just learning how to workout, go slowly. Your body is an amazing thing; it will tell you when to stop and you need to listen to it. If you work your muscles too much they will get sore. An old gym expression is “no pain – no gain”. But today we know that is just ‘insane’. If someone says this to you, just ignore them! They have no real knowledge to offer you.