On the whole, being ambitious and being happy are likely going to be in opposition to each other before the ambition is accomplished. A lot of things worthy of being described as ambitious are extremely hard by definition. There are likely to be many failures on the way. Perhaps years worth of failure. Perhaps someone's ambition will leave them crying themselves to sleep at night because they may never accomplish the goal and they hate that. Or perhaps their entire body is a mass of bruises or every muscle is sore because of how hard they are pushing their body.