Great sentence. If I had to pick it apart... 1. The comma after 'English' technically shouldn't be there (even though many natives would be tempted to put it there). 2. In this sentence "become fluent" sounds like a 1-step process. "Becoming fluent" would carry more of the nuance of an ongoing process. 3. Destructive & obstacle are both, in my opinion, excellent words in this sentence. However, used TOGETHER they don't quite feel right here. 4. "In your way" is better when that's the WHOLE phrase (Ex. "There is a huge boulder in my way.") and "on your way" is better when you add "to..." (Ex. "On your way to fame, you will encounter many challenges.") Technically speaking, 'in your way' = 'blocking you' and 'on your way' = 'on your journey.' In other words, they have completely different meanings. Funny enough, in your sentence BOTH logically make sense. The latter is simply better based on the structure and flow. Putting it all together: Being afraid or embarrassed to make mistakes while speaking is the largest obstacle on your way to becoming fluent in English. Great job!