For some I go fast

for others I'm slow.
To most people, I'm an obsession
relying on me is a well practiced lesson.

time

The answer to your riddle is "time."

Time is a concept that affects everyone, but its perception varies. For some, like when we are having fun or engaged in a thrilling activity, it seems to pass quickly. On the other hand, when we are bored or waiting for something, time can feel slow and never-ending.

The phrase "To most people, I'm an obsession" suggests that people often find themselves constantly thinking about time. We plan our activities, schedule appointments, and set deadlines based on the passage of time. It has become an essential part of our daily lives.

The final line, "relying on me is a well-practiced lesson," points to our dependence on time. We must manage our time efficiently to accomplish tasks, meet deadlines, and keep our lives organized. Time management is a crucial skill that many people strive to develop.

So, you can see that the riddle is referring to the concept of time, which affects both our perception and our daily routines.