Honestly.
Educational reasons
Honestly
this is too far to travel that the reason
Those who get fired leave the job because the boss demands it.
the pay is always unpredictable
i have not work over 3 years
You should answer the question honestly and briefly. There is no reason to go into the details on a job application of your leaving a position.
is the drive to work shorted? is the job for more money?
Looking for a shorter commute.
The hours were difficult, or it wasn't the career you were after
If you do not wish to answer honestly, then say something like "you wanted to develop your career and felt the change of job was necessary to your developmental experience".