We do want Rust to be excellent at parallel execution, but that does not mean that we don&#x27;t pay attention to single-threaded performance either. The way that we make paralell&#x2F;concurrent code better has no negative impact on single-threaded performance. In fact, sometimes you can use more efficient data structures when you know that you&#x27;re not using multiple threads, like Arc&lt;T&gt; and Rc&lt;T&gt; for example.