Have you ever noticed someone if posed a question to? Some one without long thinking would say “can not” or “do not”? Answers like this are often accompanied by our true opinions.
My point is if we say something “do not” or “can not” without thinking any longer, there is the tendency of all things will be felt closed to come after to hold and stop us to walk. I do not intend to say that we should always say “can” to everything.
Consider all things calmly, if indeed is there any clear reason? Are there any way out? If all obstacles can be solved necessarily your can answer “can” instead of “can not” to the question you are asked for. Surely having an exactly answer in a quick time need a number of exercises or experiences in the problems encountered, So do not avoid the problem. It very valuable experience.