This is an obvious lesson drilled into us through cartoons, movies, books, etc. during childhood, but only starts to take concrete applications when entering adulthood.
Some of us decide to go out on our own. Others have to stay home, to take care of others, or decide to start families of their own. Still, others decide to focus on their career by pursuing higher education, oftentimes leaning on their parents or guardian's support. Whatever your living situation, the true actualization of the phrase taking things for granted oftentimes comes during adulthood.
Why is this? Well, children grow up being naturally reliant (usually) to the point where they aren't even aware that they are reliant on someone or something. I think that we've all met at least one kid that (or have been that kid) that thinks that they are entitled to that toy, movie, video game, etc. At some point, they learn how the real world works: that everything they want in life they have to earn, that the world doesn't care about their wants and needs; and this sends a wake-up call to the individual.
However, some lessons come to some more quickly than others. Some people don't see that they aren't guaranteed to what they currently have forever. Some don't see the advantages they have had in life, until those advantages are taken away from them, and once that happens, they might never get them back.
When you have something in your life, no matter what it is, you need to take care of it, else you risk losing it. Every person has their breaking point, and you need to be aware of what that is and do everything you can to keep your interaction with that person healthy. This also applies to nonsentient things to an extent, such as a computer or car. You need to take care of and maintain anything you rely on daily (including yourself) if you plan to rely on those things in the future.
The sad thing is that most people (myself included) have to lose something in order to fully learn this lesson. As I've said earlier, nobody is entitled to anything, and you only have what you can maintain. When you don't maintain something, you lose it, and this can often happen because you didn't think you had to maintain that thing.
I know that this is all very general, but I couldn't think of anything that doesn't apply to this rule. You maintain things worthwhile to you or you lose them. It might be a very long time until you lose that thing, but the loss is inevitable.
You cannot experience the wonders of the galaxy, of loving and living and life, without putting in the necessary work, else you risk losing family members, love interests, teachers, and friends, as well as the physical stuff that, in all honestly, can be replaced with time, money, and craft.
