During any exercise and diet regimen, losing the first few pounds is often very easy. That's good because it's a great motivator when you see results right away. But as you lose more, the rate of loss, and the speed with which you see visible effects, slows down. It's hard to keep going when you aren't seeing the benefits.
But don't lose heart. It's natural that initial efforts at a certain level will get you only 80% of the way there. The other 20% is going to come harder. That's just the way things are. There are techniques that can help you get that last 20% - and, more importantly, keep 100% of the results over the long term.
Sometimes the difficulty in shedding that last 10 or 20 pounds can be loss of willpower. After achieving so much, it can be easy to say 'that is good enough'. If so, that may be ok. You may validly choose to reevaluate your goals and decide that it truly is good enough.
But beware of long term effects.
One long term effect is the difficulty of maintaining staying power for other goals. If you develop a habit of giving up before the job is complete, it becomes that much more difficult to stick with it the next time. On the upside, if you do go that last mile, the positive morale boost is a great reinforcer.
The other possibility in giving up too easily and too soon can be a greater difficulty in keeping the weight off. The earlier you let go of your original goal without achieving it, the more likely you are to gain at least some of that weight back. Sticking with it helps keep those hard earned results permanently.
There are physiological reasons as well why that last 20% can be tough. Some bodies just reach a natural plateau. It can be just a stopping point on the way to a higher peak, however. It's difficult to know for sure unless you keep climbing.
You may have slacked off of the length of exercises, or it may just require a longer period to get the same results. By analogy, it's easy to scoop peanut butter out of a full jar, but getting those last bits is harder and takes longer.
If you've been doing cardio 30 minutes a day, three days a week, you may need to extend it to four or five days. That's usually preferable to extending the length of the workout. You can begin to get close to the injury zone if you work yourself too hard during a given workout. But, you can up it to 45 minutes with minimal risk, if you judge that you still have that much more to give.
You may need to increase the intensity, at least for a while. Getting the heart rate up from 65% to 75% of maximum is one possible way. Here again, be careful of overdoing it. You don't want to achieve those weight loss goals at the cost of serious risk to your overall health.
You may have to try some new exercises. Muscles adapt. Trying some new ones works those that may have been getting less than the most strenuous workout while you were achieving that 80%.
Keep at it until you hit your final desired goal, then keep it steady. Long term results require a permanent lifestyle change.