Exercise and rest go hand in hand. You actually wear your body down during exercise and build it up with rest. Too much of one or the other can have different, yet disastrous effects. For those over thirty, it takes the body about 24 hours to fully recover from an hour of strenuous exercise, so it's a good idea to take a couple of days off a week. Daily rest is also important, get it.
Most people start off well, yet finish poorly.
A fitness program is a lifetime commitment, not a short term project. In order to keep a level of persistence, you need to reward yourself periodically. Maybe it's an extra day off from training or a piece of chocolate. It's your choice, but don't forget it.