When you commit to meditation practice, you begin on the path towards self-discovery.
And along this path you'll experience dozens of "little defeats" or adversities. Anyone that's ever worked to do something (anything) has encountered them. It's simply part of the process towards personal and spiritual growth.
Those little defeats don't point to your own inability, though. In fact, they serve as guideposts indicating that you're about to push beyond your current state to something "greater".
Your meditation practice, as well as your goals in the practice, will be unique to you. However, everyone encounters essentially the same types of adversities, or little defeats, along the way that threaten to undermine your efforts: the psychological barrier that convinces us we're being unproductive if we choose to meditate instead of work, the constant busyness that clouds our mind and leaves us asking, "what happened?" at the end of each day, and the fear that we're not practicing properly.
No matter which applies to you, eventually, you're going to lose focus. These adversities and the resulting loss of focus are a natural part of the process (of doing anything, really), so you'll need to know how to get passed them to be able to maintain a consistent practice that brings you calm and clarity.
A loss of focus could last a few hours, days, even months or worst of all if left untreated could lead you to quit on your meditation practice altogether. It's because of this that when these little defeats occur, it's important to treat them with a great sense of urgency.