Anything free is worth what you paid for it

Whenever someone offers you something for free, keep this saying in mind. This can mean anyone of 4 different things

1. The object being offered is, in fact, worthless or of negative value (i.e.: that large parcel of seaside land in Florida is all swamp)
2. You have, in fact, already paid for it, possibly with intangible goods.(i.e.: you paid for your birthday presents by being a good friend, your pension by working for 20 years, etc.)
3. You will be paying for it afterwards for some time (i.e.: The online newsletter is free but it will result in a flood of spam)
4. The cost of the free item is actually hidden among other costs. (i.e.: if the fries were really free, that burger would be half the price.)

One should note that this phrase was coined before the information age. It is not always applicable to things like software and other data that can be replicated for zero resource cost.