The phrase “to the hilt” means “all the way.” It can be used in a number of ways, as in “he lives life to the hilt,” or “she is up to the hilt in that project.” This term is widely used in most English-speaking nations, and there are undoubtedly similar phrases in other languages. A similar English term is “the whole nine yards,” which is usually roughly taken to mean “everything” or “all of it.”
This term originates from the days when swords were widely used as personal weapons. The handle of a sword is known as the “hilt,” and if a sword is plunged all the way into something, or someone, the hilt is the only part which would protrude. Therefore, when this phrase is used, it means that it has gone as far as it can possibly go, with no more give or wiggle-room. Potentially, of course, if one was really determined, the hilt of a sword could be buried in a target as well, but then the sword would be difficult to retrieve, so this would be somewhat unusual.
Depending on the context, being buried in something to the hilt might be viewed as a positive, or a negative. For example, when someone is living life this way, many people mean this as an expression of admiration, suggesting that life is being lived with no holds barred and no potential regrets about missed opportunities and lost chances. On the other hand, being involved so deeply in a project might be viewed as a negative, suggesting that someone is devoting all of his or her time to one thing at the expense of others.
While going after something to the hilt can be a good thing, it can also be dangerous. People tend to get single-minded when they are going on all-out quests, and this can cost them friendships as acquaintances may grow frustrated while waiting for their friends to realize their dreams. Single-minded approaches can also blind people to problems and issues which may be involved, and sometimes it is good to take a step back to think about a situation before delving all the way in.