What does "for ten percent of the time" mean?

Question

There is a sentence:

The study has also found that being sad for ten percent of the time is actually good for you. Let's face it. We can't be happy all the time.

I don't understand the meaning of "for ten percent of the time".
I wonder if it refers to once out of ten times. That is, it's good to be sad once in a while.
I'm not sure if my understanding is correct or not. Could you explain this, please?
This sentence is from BBC Learning English.

Answer 1

Ten percent of the time does not mean ten percent of the times.

If you read it as once out of ten times, then what are those "times"?

What the sentence says is that it's all right to be sad for ten percent of all the time you spend during a day, or your life, or whatever.

So that could be:

• 1 hour in a 10-hour period, or
• 2 hours and 24 minutes in a day, or
• 6 minutes per hour, or
• 1 year in ten, or
• 8 years in an average lifetime of 80 years

Well, actually, it is unlikely that a precise 10% is meant - ten percent of the time basically means that it is all right to be sad every now and again, as long as it doesn't become too much; 50% would mean you are sad half the time, or 100% that you are always sad, and that probably is not good for you.

So yes, your interpretation of the meaning was correct.

Answer 2

Firstly, the most literal meaning is something like, "sad six minutes every hour." But you would be right to think:

• should sorrow be distributed over a day or a life time? Is it better to be depressed for 7 years but happy the rest of the time?
• did it mean 10% of the "times"? Like if you emotionally react to something 10 times you should react sadly once?

In other words, it's actually a somewhat ridiculous sentence even if you're a native speaker, once you think about it. But not everyone thinks about it, and sometimes sentences like this can be used in advertisements and sell things. Your understanding is correct. Don't lose too much sleep over it.