Whenever you ask this person for his motivation for doing something or why he thinks something etc. you'll get an immediate response along the lines of "no reason/there is no meaning to it."
Learn English – What to call someone who always says he is doing something without a/for no reason
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Best Answer
It depends on whether you have a generally positive attitude toward the person/characteristic and think he has a good character or whether you have a generally negative attitude toward him or the characteristic and think he's got a poor character. I think you can see from the answers here that people pick one or the other.
Positive: whimsical, carefree, easy-going, light-hearted, mellow, unassuming
Negative: unmotivated, listless, careless, unfocused, devil-be-damned