Let's say your goal is to save a million dollars by the time you retire. For many people, that sounds like a Herculean task.
What are you picturing right now? If you are imagining squirreling away money for decades and holding it in cash (which has returned 0.4% after inflation* over the past 90 years), you would need to sock away a lot of money to get to a million. And along the way, your budget could be really tight.
Change your mental picture. Instead, invest in your 401(k) (or another retirement savings account) with the goal of having a million dollars in 30 to 40 years. Although it may sound like it's just semantics, it's actually much easier--especially if you start saving early--to let your investments do as much heavy lifting as possible.