There's nothing wrong with playing small - it's better than not playing at all. High expectations for success can lead to anxiety and procrastination. Playing small can break the cycle.
When we procrastinate we intentionally put off or delay a task that needs to be done, despite knowing that there may be negative consequences for not getting it done now. Approximately 80% of the population will engage in situation procrastination at some point, choosing to delay unpleasant tasks in favor of something more pleasant.