Teachers hear this every year from their students. Is it a fair question to ask? Well, it depends on how the teacher is using their influence. Is the teacher saying that knowing the electron configuration for tungsten is important regardless of what your future holds? Or is the teacher saying that the specifics of the course may not be useful, but the methods that were implemented in arriving at "learning" the concepts will be used long into adulthood? That is a fair statement, unless the teacher is only interested in compliance and little else.
In one instance, the specific subject matter is the focus (learning how to complete the square in algebra, for example), and in the other, life skills are the focus. In the life skills model, the teacher uses the subject matter to teach inquiry (asking good questions), problem solving, collaboration (working together to a shared end result), grit* (sticking with a problem until it is completely and adequately solved), creativity, and communication- maybe one of the most important, but least practiced. Effective communication includes listening. Listening for understanding is losing popularity in this world of self promotion. If those skills are what is being taught, then the answer to the original question is, "For the rest of your life."
*Grit may be the most important of these skills. See more on grit here.

When a child learns to walk, even strangers cheer for them to be successful. When a kid learns to ride a bike, strangers will stop to watch in anticipation to cheer them on. When do we stop cheering for each other? Maybe the reason we never give up the idea of walking is that we feel that the whole world is rooting for us. We continue to get up and fall down repeatedly until at some point, we figure out how to stay up more than we fall. We want to capture the first time our child is successful at walking, but we have lost interest in the falls that created that success. We should try to capture her last fall as well. Take time today to recognize a couple of things about people: find somebody doing something well for the first time (or early in the process); find somebody failing for (maybe) the last time, and celebrate all the failures that have lead to their success. Both types of recognition are necessary to keep people moving toward being successful. Go cheer somebody on!! Make a difference.

Just go ahead. Do it. Launch and don't look back. Extend yourself. Take a risk. Make it happen. Whatever you are doing is worth it if it is intended to help somebody and make this world a better place. If you go ahead and do what you have been planning and it fails... you'll get another chance...and another. When you are adding value to people and are conveying empathy, your "failures" will be excused while you come up with another way to help. Just help. We need people like you who are willing to take a risk to make this world a better place. Go ahead...jump. We're excited for the results.

If you choose to be kind to somebody, how far does that travel? How many people will be positively impacted by a kind gesture? Conversely, how many people will be negatively impacted by an insult or a negative comment? Unfortunately, we are very quick to be negative, and slow to be complimentary. Take some time today to prepare a compliment or a nice comment for somebody, and then pass it on. Be intentionally kind to somebody... An intentional act of kindness with a random recipient(s). Try it, and see how much better YOUR day is as a result. Go ahead... I dare ya'!