I'm a terrible salesman. Just out of college, I did some door-to-door sales. I had more mental breakdowns than sales.
Sometimes, though, I'll still try to use my sales skills". As I got into bridge, I started asking my parents about a lot of bidding problems. I learned that if I felt I might have overbid, I would be sure to include all my great spot cards. Instead of AQxxx in my retelling, I would say "You have the Ace, queen, EIGHT! SEVEN! two". Sure, I opened 1NT with only 13 points, but I had the 
8! I couldn't get my parents to buy that either.
While my overbidding needed as much polish as my other-sales pitches, appreciating the value of the 10s, 9s and 8s of the world is important. Take a look at this declarer play problem, and then tell me whether the 8 matters.
Contract: 6
Lead: 
Q
.
The auction:
After opening 1 with this nice hand (all of the 8s!), partner uses Jacoby 2NT. You show your heart shortness by bidding 3 and partner makes a control bid of 4
showing a first or second round control. This might be shortness, but it could also be an ace or a king. Partner’s control bid should show some slam interest after your 3 call, so you push to a slam (how, exactly, isn't so important).
The lead is the Q. Dummy comes down and we are in good shape. We have one potential loser in clubs and one potential diamond loser. If we guess well, we should make this. A slam depending on 1 of 2 finesses is going to make 75% of the time. That is plenty good, but can we do better?
You win the ace, and draw two rounds of trumps (West discards a heart). Now what? It’s generally a good idea to eliminate the heart suit, so let’s ruff a heart first, but now you are on your own. Which suit do you finesse and how do you play it?
Play the K and then take play another diamond. If East plays low, play your 8! I told you those cards were important. West will win and be endplayed into either giving a ruff and sluff, giving away the club suit, or playing into your diamond tenace. If East plays the 9 or 10, you can cover with the jack and you will still endplay West. Here’s the position after the heart ruff. If East plays the 10 and you play the J, notice how West playing another diamond would set up your 8?
If you don't see it, grab a deck and deal out the cards. I didn't put in the Q. If you try to guess it yourself, you'll be wrong, West leading clubs will allow you to take three tricks regardless of who has the queen. Notice how important it is to eliminate the heart suit so West has no easy exit cards. Whenever you have lots of trumps like this, you might think about an elimination play.
