The problem, in a nutshell, is this: We assume when we present someone with a list of our accomplishments (or with a bundle of services or products), that they will see what we’re offering additively. If going to Harvard, a prestigious internship, and mad statistical skills are all a “10” on the scale of impressiveness, and two semesters of Spanish is a “2,” then we reason that added together, this is a 10 + 10 + 10 + 2, or a “32” in impressiveness. So it makes sense to mention your minimal Spanish skills — they add to the overall picture. More is better.
Only more is not in fact better to the interviewer (or the client or buyer), because this is not how other people see what we’re offering. They don’t add up the impressiveness, they average it. They see the Big Picture — looking at the package as a whole, rather than focusing on the individual parts.
To them, this is a (10+ 10+ 10+ 2)/4 package, or an “8” in impressiveness. And if you had left off the bit about Spanish, you would have had a (10 + 10+ 10)/3, or a “10” in impressiveness. So even though logically it seems like a little Spanish is better than none, mentioning it makes you a less attractive candidate than if you’d said nothing at all.
More is actually not better, if what you are adding is of lesser quality than the rest of your offerings. Highly favorable or positive things are diminished or diluted in the eye of the beholder when they are presented in the company of only moderately favorable or positive things.

And that is presenter's paradox. Based on the PR blowback, it seems like the free U2 album was an example of that subtraction by addition at the latest Apple keynote.