Why does someone need a personal trainer? Everyone is different. People have various degrees of stamina, health issues and goals. There is no one-size-fits-all exercise plan. There can’t be. A personal trainer is familiar with the process and knows what you need to do to reach your goal. A good trainer has a sense of what you’re capable of doing and which kinds of exercises will strengthen you.
Yet, only you can be the judge of what a particular activity feels like in your body. You have to pay attention to your body to know the difference between a gentle stretch and hurting yourself.
Similarly, for spiritual development it helps to have a personal guide who knows the process, knows what it takes to get to your goal, and gets to know you well enough to sense what you need more than most people can sense these things.
Still, like physical training, even a guide can’t tell you what you’re feeling. Does this spiritual practice constitute a gentle stretch or is it hurting you? No one can answer that but you.