The ass will carry his load, but not a double load; ride not a free horse to death.

The person who never refuses is the person most likely to be ruined by the arrangement. Willingness gets read as capacity, and because there is no complaint, nothing signals that the limit has been passed until something breaks. The cost lands on the reliable one while the benefit is spread among everyone else.

If you are the willing one, refuse something this week that you would normally absorb. If you are the one handing out work, look at who has been getting the extra and ask directly what it is costing them. Do not wait for them to raise it, since that is precisely what they will not do.