This is the 3679th most frequent Spanish word.
optimista
A person who tends to see the positive side of things or expects favorable outcomes.
'Optimista' is used as a singular adjective describing the quality of being positive; 'ser' helps define it as a general approach or trait.
Ser optimista puede ayudarte a enfrentar los desafíos de la vida.
Being optimistic can help you face life's challenges.
In this sentence, 'optimista' is used as an adjective describing Clara's outlook, while 'optimismo' is used as a noun referring to the concept of optimism itself.
El optimismo de Clara demuestra que ella es muy optimista.
Clara's optimism demonstrates that she is very optimistic.
Here, 'optimistas' is the plural form of the adjective, agreeing in number with the plural subject 'Ellos' and describing their positive mindset.