Personal trainer Steve Cabral says the best way to combat this frustrating feeling is to set yourself up for a "quick win." By starting off strong -- with a super-healthy diet and perhaps some boot camp-like fitness classes -- you could lose three to five pounds in your first week, which should certainly get you excited to continue.

And when you hit those inevitable plateaus, there are a few ways to keep yourself going. Suzie Cooney, CPT, a certified personal trainer and owner of Suzie Trains Maui, says to try visualization while you're working out. "I want [my clients] to 'see' a healthy and strong body," she says. "I want them to 'see' themselves crossing the finish line as we're spinning on the bike. Visualization training is incredibly helpful." Focusing on your goal is a much better way to push yourself during a workout than focusing on how fatigued you feel or the fact that the scale hasn't moved in a week.

Get excited, because it turns out cheating on your diet can actually help your workout. Cabral says he recommends his clients have a weekly cheat meal (where you can eat whatever you want). Not only does this give you something to look forward to each week, but he says a cheat meal releases the hormone leptin, which tells the body you're not starving. The result? It can actually boost your metabolism and make you lose more weight over the next week. Just don't hop on the scale after that pizza: "You may initially go up in pounds from water weight and salt retention, but by the end of the week you'll be lower," says Cabral.

If you're feeling too sore to move the day after a workout and can't even begin to attempt another minute of exercise, it's time to rethink your strategy. Shaar says sometimes it's beneficial to end a workout a little prematurely. "It enables me to end on a high note while I still feel very energetic, it enhances my post-workout glow, and it truly makes me look forward to my next session," she says.

Spangler says this method is an especially great idea when you're just starting out. "People start giving 100 percent and then they burn out quickly," Spangler says. "You're better off starting slowly with something like strength training or a yoga class [if you're not used to exercising]. Then build up your stamina and try more challenging workouts."

While this excuse will get you out of some workouts, our experts say there are plenty of exercise methods that can actually help heal old injuries and ease body pain, which in turn can motivate you to work out even more.

If you have back, hip, or leg pain, Pilates can help strengthen your core and improve your range of motion, says Michael Leonardi, administrator at the Neurac Institute for Physical Therapy. "If you fix little nagging injuries, you can get better workouts and enhance your performance," he says.

Cabral recommends starting with stretching, interval training, and resistance training if you're overweight. Extra weight can often mess up your alignment and cause injuries if you start running or doing hard-core aerobics.

Frustration is totally normal when you're working toward a fitness goal. The key, however, is to understand how to work through it. First, Gervais says we need to realize that frustration is a secondary emotion; it's actually a reaction to hurt or fear. So ask yourself what you're afraid of, he says. "You may be fearful of some outcome, like 'All the work I'm doing is not going to pay off' or 'I'm not going to get where I want to be,'" says Gervais. When you know what's really bothering you, you can address that and make adjustments in your fitness plan to work through it.

Gervais also points out that frustration isn't actually bad. "Frustration is where growth takes place," he says. "Most people are trying on a regular basis to be comfortable, but that's not where true learning and growth happens. When you're frustrated, know that you're on the edge of the comfort/uncomfortable zone."

When you do get in that zone, Vokshoor says it's a good idea to stop, take a deep breath, and have a conversation with yourself. Remember that you're doing something great for you. Carrie Cheadle, MA, a sport and exercise mental skills coach, says it's also helpful to visualize yourself feeling strong and excited and motivated -- even when you're actually feeling the exact opposite. "Just by doing this you are planting those seeds in your brain and making it more likely that you will [continue]," she says.