"I'll do my best" is not good enough?

I read somewhere that the expression "I'll do my best" doesn't sound very positive. Is this true? If so, how do you say to assure the listner of your enthusiasm and determination to perform to the maximum extent of your ability.

Solution 1:

It depends on the degree of enthusiasm with which it is said. If it occurs as ‘I'll do my best, but I’m not promising anything’, then it doesn’t inspire a great deal of confidence. To sound more positive, a speaker would have to say something like ‘I’m going to do my very best, because I really want to help you’. Assuming it’s spoken, much depends on the tone of voice, and indeed on the facial expression, with which it is delivered.

Solution 2:

"I'll do my best", in fact, does not say that it will get done and is subjective since 'your best' may not be enough to accomplish the task, regardless of your good intentions.

If you want to give the most positive response, you would have to say something like this:

"I will get it done."

Or

"Rest assured, it will get done."