My parents had to put up with a lot on car trips. My sister and I found ways to entertain ourselves that ranged from silly to educational to combative. They were all loud. The educational games were the ones that eventually broke my parents.
As the elder child--two years older than me--she knew everything (still does).
She liked to test me on my schoolwork, but she would get frustrated by my slow responses. If she asked, "what's ten plus six?" I would start counting, "one... two... three" and get to ten, then count six more. She hated when I got them right though, so after ten plus six and five plus seven next came, "what's 70 plus 64?" I started, "One.." and my parents shouted simultaneously "NO!"
When I started playing bridge, I was mystified by the ability of experts to count every single card. My dad gave me the same advice, “You don’t have to count every card. You can know where they are to start."
You listen to the opponents have an uncontested auction:
Partner leads the 10 and dummy plays low.
This is the time to make a plan as a defender. When declaring, our plan starts by counting either winners (in notrump) or losers (in a suit contract), as a defender we start by counting the points. We have 13, and dummy has 13. Declarer opened so presumably they have 12 (although we know they might have opened with 11 or 10). That doesn’t leave much for partner. In fact, we know partner can’t have much more than 2 points.
Next we can look at shape. The opponents are probably in a 4-4 trump fit (declarer bid hearts second after all) so partner probably has three hearts. Declarer also opened 1. That means that with our five and dummy’s two, partner has at most 1 spade. With 3 or 4 cards in the majors partner must have a lot of clubs and diamonds. Without all of this information our right play is to play low. Once we have all this information, however, we should rethink our plan.
If the 10 wins (partner would lead the 10 from Q1098 as the top of an interior sequence), partner could continue diamonds, but it is a distinct possibility that declarer can ruff the next one. In that case, declarer will draw trump and play on spades, losing just the 3 aces. If the 10 loses, it could similarly be to a singleton Q, which could be catastrophic - now we only take two aces.
Instead, we should win this trick with the ace. Now, we should play the ace of spades and give partner a spade ruff with the 2 of spades. That is, we should do that if we trust partner to read our 2 as a suit preference signal for clubs. If partner doesn't always pay attention to our cards (bad partner!) we might cash the ace of clubs before playing the ace of spades and a spade. This will eliminate any chance of partner guessing wrong. We might lose a trick if declarer was originally void in clubs.