“I can’t.” No employer wants to hear that you cannot do something. Rather than saying you cannot or do not have the skills they need, say something like “That is an area I have always wanted to learn more about.”
“No.” Saying “no” to an employer regarding just about any matter is going to get you into trouble with your career. Employers want to hire “YES” people. Always figure out how to make something work rather than how it cannot work.
“I will try my best.” There is no try in business, there is only do. You either give something your all and succeed or you give it your all and fail. There is no in between.
“I hope it will work out.” People who use words like “hope” and “try” are typically people who do not go on to huge success in business. It is important that you commit to an action rather than “hoping” it turns out.
“It was not my fault…” People who are unwilling to take responsibility for their actions are often seen as victims and/or martyrs and are rarely promoted. Always take responsibility, even if it was not your fault and then figure out how to make whatever the problem was right.