Why do people refuse to speak the truth?

Some one had raised a question some days back as to why do people refuse to speak the truth?

The question was thought provoking and somehow it drew my attention, so I thought about it. What I could think of is a personal assessment, obviously every one will have his own reasoning. But mine is given below:

• Firstly and quite obviously people refuse to speak the truth to hide a mistake or a lapse. This happens due to the fear of punishment.
  
• One very common case amongst people to avoid speaking the truth is to keep the other person in good humour. It assumes they believe that the other person may not take the truth in right spirit.
  
• The third type is complicated, as the concept of truth will depend upon what the seeker may (& wrongly) perceive as truth. Here, there can be a lot of deception if one continues to keep the seeker in dark by continuing to explain him what the seeker believes to be truth and take advantage of speaker's misconceived notion. Sycophancy is a milder form of this category.
  
• The fourth type is most beautiful and the saddest also, as the truth is too sacred to the speaker and there is fear in his mind whether his truth will be perceived with same sanctity. These truths are easily identifiable but difficult to elicit as this will require a lot of reassurance for the speaker to speak those. Here also the reason is the fear of punishment albeit the punishment is not physical but emotional or spiritual.
  
• Poorly placed Mercury in a horoscope can make a person a habitual false speaker. But this may be different from the case of ‘not speaking the truth’ which is different from lying. Speaking falsely is a wide genre which may originate due to financial or other constraints.