Who Am I?

Untuk memeriahkan sedikit minda ahli jabatan yang sentiasa sibuk tu, cuba lah jawab teka teki ini.

I am your constant companion.
I am your greatest helper and your heaviest burden.
I will push you onward or drag you down to failure. I am completely at your command.
Half of the things you do might as well turn over to me. Show me exactly how you want something done and after a few lessons I will do it automatically.
I am the servant of all great man and alas, of all the failures as well.
Those who are great, I have made great. Those who are failures, I have made failures.
I am not a machine but I work with all the precision of a machine plus the intelligence of a man.
You may run me for profit or run me for ruin, it makes no difference to me.
Take me, train me, be firm with me, - and I will place the world at your feet.
Be easy with me and I will destroy you.

WHO AM I?