It's no secret that Wal-Mart (NYSE:WMT) has been struggling over the last few years. Thanks to increased competition from the likes of Amazon.com (NASDAQ:AMZN) and Costco (NASDAQ:COST), same-store sales at the nation's largest retailer have fallen at an alarming rate. Despite this, Motley Fool contributor John Maxfield thinks there's one big reason that investors can still be confident about the future of the company.