the word that makes my life short!

i am myanmar and inherently i got the dellima of "saying Yes". i just want to say no but "yes" always comes out of my mouth. when my friends out there ask to borrow money for lunch and if they ask me explain abt the manufacturing strategies, the internetworking and political economics, it may not be likely the problems within these contexts. but yet to the others, "yes" is the most dillema for me. according to my working nature, i need the long term plans and strategic goals for the determined future. so i always make them up, but when it comes to the day-to-days, i couldn't get the things ( priorities ) done. i know "Yes" can make my focus diffuse and only "No" can let me concentrate on my priorities. but i couldnt simply accomplish to say "No". why .......