What should not lapse even for a millisecond?
The
Blessed Buddha once said:
Sambādhe vāpi vindanti, dhammam nibbānapattiyā
ye satim paccalatthamsu sammā te susamāhitā.
Focused Awareness:
Even when obstacles crowd in, the state of Nibbāna
can be won by
those who establish awareness by a full, even, and steady
focus ...
What is Right Awareness?

More on this precious mental quality of
Awareness (Sati):
https://What-Buddha-Said.net/drops/Sati_Studies.htm
https://What-Buddha-Said.net/drops/Causes_of_sati.htm
https://What-Buddha-Said.net/drops/III/Sati_Summary.htm
https://What-Buddha-Said.net/drops/IV/Sati_in_Solitude.htm