Maartje Sofie compares hidden emotions to Tupperware crammed into a kitchen cupboard. It's a small, homely image, and that's what makes it work. Nobody thinks much about a cupboard until something goes wrong with it, and the speaker suggests feelings behave the same way. They get packed away neatly, out of sight, and life carries on as if everything is under control.
The trouble comes in the second stanza, where the speaker imagines a day when "you forget how full it is." The "you" is interesting. It could be the speaker talking to themselves, or someone else who opens the door without realising what they're about to unleash. Then the poem speeds up: one quick glance inside, and everything crashes down.
The mood is tense and a little anxious, though quietly funny in its ordinary imagery. The speaker seems to feel that holding everything in works only until it doesn't, and that the collapse will arrive suddenly and without warning.