Ambition is not a good thing. An ambitious person decides for an action because he thinks the action will lead to his success. A good person decides for an action because he thinks that the world will be a better or more beautiful place on account of his taking that action as opposed to an alternative action. Of course, you could say that a person can be ambitious to behave good and improve the world, but my impression as an English spaker is that the word "ambitious" as typically used does not denote such moral motives; at any rate, I'm not interested in getting in an argument about what the word means, which is not likely to be a particularly interesting argument.
There is a sense in which ambition is not practical, either. Ambition, it seems to me, connotes having a goal. When, for example, a female decides to have sex with some guy, it is important for her to set that as a goal before some competitor of her would-be lover sees her dreamy lovey state and forcibly sodomizes her to thwart his competition. Similarly, one can think of other behaviors which once decided upon could cause others to try to emotionally abuse you to make you behave otherwise. For instance, if you are fighting getting raped, you will likely set as a goal the elimination of the attempted rapist (at least as a threat, probably even more). Having that goal in such a situation is fitting inasmuch as abuse can have addictive qualities that tend to induce extreme excess sympathy for the abuser in the abused. It's not everyday that one gets abused or molested, though. Insanity is largely having an excess of anti-abuse emotion in non-abuse situations. The tendency to set excess goals as in the ambitious is a type of insanity, more commonly excessive (at least in the non-sexual realm) than the opposite tendency.
A good many religions probably get a good deal of their popularity from their tendency to squash ambition. Consider Jesus' parable about the lillies of the field, how they neither toil nor spin, etc. Or again, consider the third of Buddha's Four Noble truths, that vanity can be ended only with the ending of all desire. Taoism probably is the most purely anti-desire: "There is no greater guilt than to sanction ambition; neither is there any greater calamity than to be disconted with one's lot [Tao-Teh-king]." It is relevant that this anti-goal aspect of religion tends to have its strongest appeal to intellectuals and the higher classes. Common people are much less insulated from the disgusting addictions against which ambition and goals afford quite reasonable protection. Apparently, the anti-desire element of Hinduish is strongest in Brahmanic Hinduism (which emphasises the nihilistic Upanishads), but Vishnu and Shiva worship are more favored by the common people of India. The kind of Taoism that has popular appeal is very far from Lao-tzu, involving alchemy, magical interpretations, etc. It's shouldn't be surprising, really, that Taoism, a religion that tells one to not fret about becoming corrupted, would have very greatly tended to become corrupted.
It's amusing that nowadays there are so many popular self-help writers pushing enthusiam and goals to make you successful in life, business, etc. It's an aspect of something larger, I'm afraid. Enthusiasm by its very nature in the short-term leads to success. It will wear you out in the long run and lead to failure in other parts of your life, but yeah, generaly being enthusiastic about something helps you deal with it in the short-run. And so managers are forever trying to push some motivation or manipulation or whatever that will make their employees more enthusiastic about their pencil-pushing or whatever. More of a one-day-at-a-time approach is generally best when dealing with the ordinary events of life, IMO. It's curious that enthusiasm is so much more praised than cool deliberation now. I don't think 60 years ago it was so much like that. Why are there no prototypically cool actors like Humphery Bogart now?
It's easy to see that in Iraq, the reason the defense department underestimated the danger of looting is that they were too fixated on the goal of military victory. Goals and ambition toward these goals cause problems.
I was just thinking the other day that the best mathematical writing, e.g., (hopefully, I'm reading it now) Shoenfield's book on mathematical logic, is done in a kind of jazzy, I'm-doing-this-and-(why-not?)-devoted-my-life-to-it-because-all-else-in-life-is-vanity-but-this-isn't-so-important-that-I'm-not-half-asleep-while-writing-it kind of style. It's an uncorrupted Taoist attitude that as my theories suggest seems to be associated with professors at expensive laid-back private universities like Duke or Princeton (as opposed to state schools). It just occured to me the other day it would be interesting to try to meld that viewpoint with a very deep and inclusive Van-Gogh kind of outlook on life.