I have a single entry visa for Italy and I planned to stay for 2 weeks. I got the visa valid for a 24-day period, and duration of stay is 10 days.
Can I stay more than the duration of stay, for 14 days instead of 10?
They gave you a period of validity which is longer than the duration of stay. That means you are free to adjust your travel dates by a few days as long as the total length is less than 10 days. (As Zach wrote, the first and last days count full.)
That's for your and their convenience. If a business meeting is rescheduled by a few days, or if you decide to take a different flight, you do not have to apply for a new visa. But you cannot increase the stay beyond those 10 days.
No. Your visa only allows you to stay for 10 days (any calendar day you are in the Schengen area counts as "a day" for this purpose). While you, of course, physically can stay longer, overstaying your visa is prohibited by law. If you do so, it could be significantly harder to obtain visas in the future (both to Schengen countries and other countries) and you could be fined.
As discussed in this related answer, you should stay for the period permitted by your visa or go back to the consulate that issued it and ask for a one with a longer duration. If you submitted an itinerary and documents for a 14 day trip, then you can ask if there has been a mistake and request that they correct (or reissue) your visa for the correct duration.