This is the 171st most frequent Spanish word.
misma
"Same" or "self" (feminine form).
Here, 'misma' is used as an adjective to emphasize that it is the very same girl being referred to as before.
La misma chica vino ayer a la tienda.
The same girl came to the store yesterday.
'Misma' here is used as an adjective to indicate possession or direct emphasis on the motivation itself.
Siempre quiero mejorar, esa es mi misma motivación.
I always want to improve, that is my very motivation.
In this case, 'misma' acts as a pronoun indicating sameness or similarity with the prior year.