Sincerity is thrown around quiet a bit without much understanding for what it means.  Lets provide a clear cut definition of sincerity.  It is ones honest opinion on thoughts and feelings.  They are generally your own and should be used very cautiously.  It is imperative that you ensure that your sincerity does not adversely affect someone to the point of negativity.  If you have provided someone else a negative feeling, than your sincerity was in vain.  I understand how it can be considered a rough point but keep yourself in a sincerity “hole” and ensure that your sincerity doesn’t make others feel bad.