I usually twist this into "memento mori, quoque uiuere" (remember [that you'll] die, also [that you'll] live).
Like, not trying to become worm food full of regrets is nice and dandy, but remember that you'll suffer the consequences of a few of your actions while you're still alive.
There's no "must": it states for a fact that you're to die, not that you should/need/must.
A rough translation would be "remember that you'll die", or "remember that you are to die" (keeping the infinitive). Or even "remember death", it's close enough in spirit.
Yeah, but I was quoting a very influential song in English hip hop by The Streets with the same name and about the saying.
TLDL:
The phrase is about realizing wealth and life isnt permanent, eventually it will be gone.
Not caring about money when poor leads to a shitty life, but not caring about money because you're famous and driving a Ferrari is a hell of a lot better.
The phrase makes poor people docile, you can only not care about material wealth when you have enough that you don't need to worry about it.
This, my friend, is an overly cynical take. You can apply it to your life in any way that serves you. You can imagine it as a good reminder to live life to the fullest, to not let your ego run away from reality, or to give perspective on all the little things we worry about when we consider how many weeks we have left on this planet.