Idleness is one of the most demonized behaviors in the west. The guilt people get for being idle, whether self-induced or handed to them by family and peers, causes them to go to university and major in something they don't care about.
Idleness isn't the enemy. It's restlessness and constant, arbitrary activity.
How often do you hear parents say today, 'At least my kids are reading SOMETHING'? 'At least they're getting out of the house, even if it is Pokemon.'
Seizeless activity, in and of itself, without thought behind it, is fear of death. Every activity requires its own degree of thought. Sometimes it's better to quiet your mind altogether. Your intellect is a tool that can wear itself out just like your body.
No two people are the same. everyone has a different level of ambition. Figure out the proper nutrition for your mind and body and ambition will take care of itself. You can't favor ambition over idleness, as they complete each other.