It is okay to say, “No!” to someone.  You do not want to go there too quickly.  You have to try but everyone has limitations.  “No”, states you have reached your limit and you can’t go further.  Everyone has limitations.  Nevertheless, make sure you have given it your best or simply can’t.  You always have to try and never forget that.  You can’t go to “no” too quickly or automatically.  “No” has to mean “no.”