There are dozens of techniques in mma fighting and few can master them all. Most guys come from one of the main disciplines; boxing, wrestling, Brazilian Jiu Jitsu etc and so they have distinct strengths and weaknesses. A wrestler will want to get in close and get to the floor at the first opportunity, a boxer will prefer to stay upright and use a combination of hands and knees to exercise control of the fight. Whoever you are and whatever your background you will need to work on your core strength to maximise this area but you will also and perhaps, more importantly, need to hone your skills in the areas where you are weak.
Everyone has weaknesses no matter how seemingly unbeatable and it's ensuring that you have a fully rounded training program that will ultimately bring you success in your fighting career. Turning weakness into strength is key; how many times have you witnessed fighters who look like they're beaten suddenly turning the tables by using Houdini style escape moves and who have the ability to apply and execute brutal locks, even when in a vulnerable position.