There are various reasons, one  
is enhanced
 the ability to understand about the world and the nature of the world. After that they are tend to believe that these  
ambitions
 aren't worthy and they have other things to do like  
improve
 their mental power and engage in kind of meditation like that.  
on the other hand
 when they mature, the desire for materialistic things could  
be declined
 and tend to  
love
 for a simple Lifestyle. that's why the high  
ambition
 would  
be disappeared
 when we  
come
 to the adult age from our youthful age. According to my point of view I believe that you should have an  
ambition
 until your death. Without an  
ambition
 it is difficult to survive and grow
There are various reasons, one  
is enhanced
 the ability to understand about the world and the nature of the world. After that they are tend to believe that these  
ambitions
 aren't worthy and they have other things to do like  
improve
 their mental power and engage in kind of meditation like that.  
on the other hand
 when they mature, the desire for materialistic things could  
be declined
 and tend to  
love
 for a simple Lifestyle. that's why the high  
ambition
 would  
be disappeared
 when we  
come
 to the adult age from our youthful age. According to my point of view I believe that you should have an  
ambition
 until your death. Without an  
ambition
 it is difficult to survive and grow