When people announce this, what they really mean is that it does not cost you money to do the thing. Invariably, that thing you could do will cost you time. It might cost in terms of emotional labour. It costs you zero money to leave a book review, but it does cost you time and mental effort and you might not have those resources to spare right now. It costs you no money to smile, but if you are exhausted, in pain or dealing with grief, it might also cost you far more than you can afford to pay.
The idea of the action that costs nothing is a key one in terms of patriarchy and capitalism. On the capitalism side, it keeps us focused on seeing money and payment as the only measure that matters. No great value should be put on anything non-economic. This encourages us to undervalue non-economic activity. However, that non-economic activity – domestic work, emotional labour etc is often what women are expected to provide.
Saying ‘it costs you nothing’ creates emotional pressure to give, hides the very idea that a cost exists, and devalues the person doing the non-economic thing.
It’s also important to consider that costs are not the same for everyone. If I am in a good mood, a bit of performative smiling isn’t that expensive. Other times, it could break me, because of the overload, the emotional effort, the cost of masking and so forth. What it costs a happy, pain free, untroubled person who has plenty of resources is not what it costs someone in pain and in crisis to do the same thing. What any given thing costs you is not what it costs someone else and personal experience is not a fair measure.
Energy costs are a big deal for anyone who does not have enough energy to get through a regular day. Emotional costs are a big deal for anyone who is already overwhelmed and unwell. Masking costs are huge for people who are neurodiverse.
Anything that is worth something will also cost something – in time and effort, in care and attention, in what you won’t be able to do because you did this instead. Money is not a meaningful measure of cost. If you want someone to do something for you, perhaps the right place to start is in acknowledging the value of that thing, not downplaying it for emotional leverage.