Error where the coin has the obverse on both sides! Why?

Hello, i bought this coin in a lot, and it has this weird error where the reverse is just the obverse but as an incuse instead of relief. 
How can this happen? Is it rare? Does anyone have similar coins? Does it add to the value of the coin?

In other words, should i be happy that it is like this or rather have wished it had the cow reverse.
N#445062

Carol51

Hello, i bought this coin in a lot, and it has this weird error where the reverse is just the obverse but as an incuse instead of relief. 
How can this happen? Is it rare? Does anyone have similar coins? Does it add to the value of the coin?

In other words, should i be happy that it is like this or rather have wished it had the cow reverse.
N#445062

Turns out its a brockage, one coin was struck and when the worker added a new blank disk he forgot to remove the first coin and hammered them together, the design of the first coin stamping the blank side of the second. Really cool!

yes it is. thanks for sharing!