"Sound" means it is already justified--by the facts that
1. it met the requirements for 'validity', and
2. it is a true statement from two true premises (which is not necessarily true of 'valid').
If someone thinks it is not sound, s/he will have to provide the counter-argument; and since you cannot know in advance what that will be, you can only advance your own argument, making certain it is in your opinion 'sound'.
But if what you want is the justification that IT IS sound, you will be giving an explanation about logic more than about the topic of the statement.
Fear of something is an opposite of love. Today people fear terrorism, financial difficulties, acts of nature with global warming, children being kidnapped, etc. These are all possibilities that could very well cause people to sink. Some people retreat by eliminating possible scenarios that could alleviate their involvement in any fearful situations. That doesn't seem like a could solution. It leaves you with a burning desire that is unfulfilled.
I think preparation is the best answer to handle fear. Become educated in an area and plan. When you are familiar with these challenges you can at least work on solutions. If you do the best you can after research and planning, forget fear. Replace it with this is what life is and enjoy everyday. Don't wait for the judgment day to say I should have done it.