Many decades ago, there were someone who said “Boys, be ambitious” and this means that in order to realize ambitions boys should make efforts and will grow up. But if boys think it will be a little bit difficult to realize their ambitions before showing their ambitions, it is easy to give up their ambitions and stop to make efforts and to grow up.
I think it might be better to say, “Boys, show your ambitions”. By showing ambitions, it will be much difficult to give up their ambitions. For the people who would like to grow up in their life, Nowadays, I think it is necessary to have a brave mind to show their ambitions. For example, to swear eternal love in the wedding party is very important commitment.