There used to be a time when your code got faster every year automatically, as processors got better and better. But nowadays, as Herb Sutter famously stated, The Free Lunch Is Over (http://www.gotw.ca/publications/concurrency-ddj.htm). The age of not better, but more numerous processor cores arrived a long time ago. Not all programming languages are well suited for this radical change towards omnipresent concurrency.
Rust was designed with exactly this problem in mind. Its borrow checker makes sure that most concurrent algorithms work fine. It goes even further: your code won't even compile if it's not parallelizable, even if you don't yet use more than one thread. Because of these unique guarantees, one of Rust's main selling points has been dubbed fearless concurrency.
And we are about to find out why.