Every person has their limitations concerning the weight one can lift or carry bags, and there comes the point that there is no more one can bear. One can build resilience and capacity as you take on more, yet limits will prevail.
While we can agree on the physical limitations, how often do we ignore our mental and emotional boundaries? The person who takes on more work to add to their load and bear the trouble of others. It adds up fast, and we seem to ignore the weight that it adds to us. With the physical limitations, we feel the consequences immediately, yet our mental threshold does not snap instantly, forcing us to stop. Instead, it increases slowly, and when we finally do break, it has more significant adverse consequences, and the recovery may be longer.
In all facets of our lives, one can only carry so much load and no more. We have limits. Say no to be strong, and be assertive with your no.