noun, noun which may take the genitive case particle 'no', na-adjective
nervous temperament; worry-prone nature; pessimistic disposition
Describes a person who tends to worry excessively, overthink, or expect the worst. Often used to characterize someone's inherent nature.
彼は苦労性で、小さなことでもすぐ心配する。
He has a worry-prone nature and gets anxious over even small things.
苦労性の人は、なかなか楽観的になれない。
People with a pessimistic disposition find it hard to be optimistic.
楽観的 means 'optimistic', the opposite of the pessimistic tendency implied by 苦労性.
Compound of 苦労 (hardship, worry) and 性 (nature, disposition). The exact historical derivation is uncertain, but the word transparently means 'a nature inclined toward worry and hardship'.