Both sides vulnerable.  
West deals.
                              North
                              S: 10 8 6 3         
                              H: Q 7 5 2     
                              D: A 5 4       
                              C: K 3     
            West                             East
            S: A J 7 4 2                     S: K Q 9        
            H: A                             H: K 10 8 4   
            D: 10 9 8                        D: J 7 3 2           
            C: 8 6 4 2                       C: 10 7        
                              South                         
                              S: 5     
                              H: J 9 6 3    
                              D: K Q 6     
                              C: A Q J 9 5
          The Bidding:  
                   West   North     East   South                  
                   Pass    Pass     Pass    1C  
                   1S      Dbl      Pass    2H  
                   Pass    Pass      2S     3H  
                   Pass    4H     (All Pass)
          Opening lead: AS
     The North-South pair had a long discussion about what went
wrong after this contract was set two tricks for minus 200 and a
poor match point result.
     Everything was pretty normal until East made a competitive
two spade bid.  Now, two spades was going to make or go down one
at the most.  It is probably too close for either North or South
to make a penalty double.  So the spotlight turns to South.  Is
three hearts reasonable at that point?
     In a competitive auction there is a big difference between
an action that should be taken in the direct seat compared to an
action that is reasonable in the balance seat.  
     At each opportunity to bid, you have to consider your position
and the prior bidding.  If your RHO (right hand opponent) has 
made a bid, you are in the direct seat.  This means that if you
pass your partner will still have a chance to bid before the
auction ends.  If this is the case, pass simply means that you
have no new or additional information to add to the bidding
analysis.  
     South is looking at a normal opening bid with five clubs 
and four hearts.  With distribution, you could count the hand 
as being worth 15 points.  Also, you more queens and jacks
than aces or kings - so maybe 13 is a more reasonable evaluation.    
     Let's look at North.  When the bidding comes around (with
two spades by East being the last bid) he will have to decide
whether to defend or bid three hearts.  He is a passed hand and 
then made a negative double showing at least five or six points 
and four cards in the unbid major and tolerance for diamonds.  
     The vulnerability along with weak hearts and a four card 
spade holding should encourage him to pass - three hearts is
possible but South will have to play perfectly to bring this 
contract home.  
     The point is that the decision is being made from the
correct hand and the contract will be reasonable - in either
case.