This quote means that in order to love something, you must accept that one day you may not be able to have it or keep it around anymore. This could mean that the person or thing you love could leave, pass away, be taken away, or simply disappear. Accepting this potential loss is an important part of loving something and being able to fully appreciate it and the time you have with it. This means that it is important to cherish the moments when the loved one or thing is still around, while also preparing yourself in case it someday needs to be let go.