Zero dollars does not feel like just another price.
If something costs one dollar, your brain still has to ask whether it is worth one dollar.
If the price drops to zero, that question changes.
There is no money to lose.
This is sometimes called the zero-price effect
People often react disproportionately strongly when a price moves from a small positive amount to zero.
A drop from $2 to $1 is a one-dollar improvement.
A drop from $1 to free is also a one-dollar improvement.
Psychologically, the second change can feel much larger.
Free removes one kind of risk
If you pay nothing, you cannot lose money on the item itself.
That can make trying something feel much safer.
If you dislike the sample, app, or trial, at least you did not pay cash for it.
Why does “buy one, get one free” sound so good?
The word free gets its own spotlight.
An equivalent percentage discount may produce the same mathematical value.
But “free” feels like a separate reward rather than just a lower price.
That framing can make the deal more exciting.
Is free actually free?
Sometimes.
Sometimes not.
A free service may cost attention, personal information, time, or exposure to advertising.
A free item may require another purchase.
A free trial may turn into a paid subscription if you forget to cancel.
Zero dollars is not always zero cost.
Why do marketers love the word?
Because it attracts attention and reduces resistance.
People who would ignore a small discount may stop for something free.
The word simplifies the decision.
How can you evaluate a free offer?
Ask what you are actually giving up.
Money?
Time?
Data?
A future obligation?
If the answer is truly nothing important, free can be a great deal.
If not, the zero-price feeling may be hiding the real cost.
Free can be a very good deal.
It can also be a very effective way to get your brain to stop asking what the deal actually is.
A related piece of human behavior appears in Why do free samples make us more likely to buy?, where the brain handles another everyday judgment or response.
And that’s the short explanation.
Related explanations: Why do free samples make us more likely to buy?, Why do we want things more when they are scarce?, and Why do we stick with the default option?