FROM MY EXPERIENCE of training athletes, I know they need fitness because good physical fitness will increase their focus, efficiency, and body composition and reduce injury.
Fitness in mid-life is different. It is about mindset, and the discipline to exercise is not necessarily there in people who need to do it the most.
Clarity is power; if you want to be healthy, you've got to decide what healthy is. You create your ideal health goal, then work toward it and dismiss the idea of failure.
When you are setting fitness objectives, the goal to lose or put on weight might is not enough. It must be specific (how much weight) and within a realistic time frame; otherwise, you will fail. Frame your intention positively 'I want to love the way I look'. 'I want to love the feeling it will give me. 'I'm going to feel positive when people talk about my determination to achieve my goal.'
While your goal should be challenging, it shouldn't be unrealistic. For example, if you've never run before, it's unreasonable to expect to run a marathon in a month. Nor is it realistic to think that walking for 30 minutes a day will give you a beach body. Setting goals such as these is worthless and causes you to give up when you fail to achieve them.
Also, failure most likely results from not being sufficiently motivated when you want to exercise but don't. You will only achieve something if you want it; it's as simple as that. My training identifies three essential components: identifying the intention /goal, learning the exercise, and reinforcing the self-image.
Finally, an App can help you get started on the path to fitness, but it's not going to be what forces you to exercise. Discipline is. It's the essential component of fitness.