Challenge

Martial arts are quite demanding to learn; requiring the student to significantly increase their strength, agility, endurance and speed.
The challenges are both physical and mental.
A casual approach will not work.
Body, mind and emotions need to be conditioned and honed through sustained, regular practice.
The training must involve a wide range of challenging martial concerns; increasing in difficulty as the student becomes more adept. 
To possess combat skills, you must train combat skills.