Nobody appreciates a phase while they're inside it. That's what this is pointing at — not a second, but the stretch of life you're currently in.
People are famously nostalgic for exactly the periods they spent wishing away. The cramped flat. The underpaid year. The season with small children and no sleep. Later, it's the good part of the story.
There's no way to fully avoid that, but you can shave the edges off it, by treating the present chapter as one that will end.
What will you miss about this one? Answer honestly, then go do that thing today.