Question: What stops a man to ask the ultimate question to his lady love "Will U Marry Me?"? 

Answer: Just the simple fear of "till death do you part".  That is the ultimate fear.  That is, until you have found that one true love.  Then, it is easy, because you mean it.  It is the same as "I LOVE YOU".  I can not say it unless i mean it.  My wife and kids are the only ones who have ever heard me say it.
This question from the Yahoo Q&A forum is categorized in the topic: Family & Relationships