When it comes to building muscle, losing fat and getting into shape, the biggest problem for most people is simply sticking to their training goals. This is called 'adherence' in the industry and simply means your ability to stick at a training program long enough to see the results that you need.
Even a poorly designed workout can help you to build muscle and get results if you stick at it. And it is much better to perform a bad workout for a long period of time than it is to perform the best workout possible for a day and then give up.
But this is something a lot of people don't really consider when they plan to get into shape. Too often they will come up with routines that involve training for an hour each session, five times a week. If you're already feeling too tired to be particularly active, if you're already stressed with work trying to fit in five hours of exercise a week is a huge ask. This is particularly true when you consider that you're probably going to have to travel to the gym as well, get washed, change clothes etc.