A tired worker who asks for help beats a proud one who drops the box.

Asking for help is a calculation, not a confession. A dropped box costs more than a moment of looking less capable, and everyone around you can see the difference between somebody managing their limits and somebody pretending not to have any. Pride is expensive when it is carrying something heavy. The ask is usually smaller than you fear.

Next time you are near your limit, say so before the thing goes wrong rather than after. Use a plain sentence: this is heavier than I can manage alone. Offer the same when you see somebody else struggling with it.