It’s about the intention you set with “try” versus “do”. I believe, whether you intend it or not, “try” gives you a subconscious escape from the amount of effort you will exert in your attempt. “Try” implies it’s OK to not succeed. “Try” is passive. Even though DOING may still result in failure, and failure is acceptable, when you say, “I am going to DO this,” your intention is fully committed.