Don't be afraid of being wrong.
The only real mistake you can make is to NOT define your terms.
If good thinking requires anything it definitely requires precision and precision means: define.
For example: man is a rational animal (page 42, pbk). Rational is "differentia", and animal is "genus": the two minimal "things" a good definition has to possess.
Remember: Ayn Rand said (somewhere, and if you think about it it is true): the main purpose of language is to help you think.
So, make sure your definitions have a genus and differentia for starters and you will stay on the road to mental health. If you are on this road, stay on it and if you are off it, check your definitions and get back on and make corrections and improvements as you travel its main roads and many side streets inside the safety and security of your own mind's precisely defined, reality-matching terms.*
no mind --that includes mine and yours-- is any better than the precision of its concepts.
And to also repeat, some precision is better than none and the best precision is the one that reflects reality in a non-contradictory fashion while integrating the current state of all that is known about a topic.
For example: Mental health is the unobstructed capacity for reality bound cognitive functioning --and the exercise of this capacity. (page 101, pbk) and by extension, mental illness is the sustained impairment of this capacity.*