The push-up is a basic bodyweight exercise that should be mastered for anyone on a resistance training program. Before the invention of exercise weights, there was what we call the “body.” It’s the first thing you must learn to control and move properly before graduating to extensive weightlifting and complex exercises. You may not be able to perform 100 perfect push-ups continuously, which would require extensive stamina, but strive to at least perform a handful at a time to start. They are difficult for a lot of people for a number of reasons. Strength to weight ratio can be a big problem for anyone when it comes to gymnastics; the heavier I am, the more force I have to apply to move myself. For a well-rounded state of fitness, I should be able to push and pull my body in a variety of ways efficiently and correctly. If I’m on the heavier side and relatively weak in comparison, I need to take steps to increase my strength to match my size. Or, I need to trim a little fat and increase lean muscle mass. (It can depend on your sport, or your specific goals, etc). Again, for well-balanced fitness, it also doesn't really matter if you can deadlift 350 lbs, and are unable to perform a proper push-up; there is a glaring imbalance. Strengthening your push-up can only increase your deadlift. Compared to the bench press, the push-up requires you to press, while actively forcing you to engage and stabilize your core muscles: all of those abdominal muscles, the back, as well as the hip flexor muscles, and hip/glutes. Yep, there is a lot going in a push-up. So, diagnose the problem. It is probably a combination of a few things. Are you sagging in the middle? Strengthen your core ; there is an almost limitless amount of exercises and drills you can perform to strengthen and stabilize this area. Plank holds and variations are very helpful. Learn to the hold the correct position (squeeze abs, tighten butt), and the push-up will appear. Can’t press out? Strengthen your upper body. Using appropriately loaded external resistance (KB, dumbbell, barbell) can be helpful for gaining strength, but make sure you are maintaining strict form. Work on a variety of pulling movements as well, not just pressing. (Every strong muscle needs an equally strong antagonist, or "opposing" muscle for balance and proper function.) Use these tools to assist you, but don’t forget about practicing the push-up itself on regular basis. Don’t get caught using a bunch of weights if you can’t control your own body correctly. It takes practice. It’s that simple. Put in the time on a regular basis and you see results. It doesn't need to be complicated. Watching a TV show? Hold a plank or do some push-ups during the commercial. Wow, that’s remarkably easy to do. Practice makes permanent. If you are given the task of 100 push-ups within a workout, you will never get any better by performing 100 “ground humps” for time. You practice with strict form, scaling or modifying however you need, and your body will gain the correct muscle memory of the movement and get stronger in the process. Never practice anything correctly, and you will only ingrain the bad habits further. This not only applies to push-ups, but everything.