Bridge isn’t fair.
One time, playing in the qualifying round of a national event, my partner and I bid to a flawed 4
contract. It got doubled, and I went down one. Checking the scores later, almost every pair in the room was in 4 down one, and I was the only one doubled. We’ve all been there.
My complaint: the person who doubled me was my mother.
At the table, your partner is your only family, and you must work to keep the opponents unhappy--only by playing well, of course. You should never try to intimidate or make players feel unwelcome by having a bad attitude.
If you double your opponents when they walk into trouble, you'll make their lives difficult.
You, East hold:
105 AQ109 
543 
K1098
The auction goes:
| West | North | East | South |
|---|---|---|---|
| 1NT | |||
| Pass | 2 |
Pass | 2 |
| Pass | 2NT | Pass | 3NT |
| Pass | Pass | ? |
You should double here. This double is for penalties. There are a few reasons: 1) You know they don't have a ton extra (limited hand opposite limited hand), 2) You know that nothing is splitting well for them--you have hearts over dummy and partner has spades over declarer
3) Double on this auction suggests a lead of dummy's suit (hearts) which is what you'd like from partner
If most of the room is in 3NT-1, you're going to do very well to defend against 3NTx-1
Here's another hand where you should strongly suspect your opponents are going down:
You are East.
5 A76 A10876 J1098
You are East and your opponents bid:
| West | North | East | South |
|---|---|---|---|
| 1 |
Pass | 2 |
|
| Pass | 3 |
Pass | 3 |
| Pass | 4 |
? | |
Before you make your bid, let me ask: what are you going to lead?
You need to pay attention to auctions. Here you know your opponents have a diamond and spade fit. Well, that's fine. You know that partner can ruff diamonds. You expect to take the first four tricks: A, 10 (a suit preference card) which partner ruffs, partner pays attention and returns a heart to the A, and another ruff.
When you know the opponents are in trouble, get that extra bonus for penalizing them or you won't get to take advantage of those times when life gives you a chance to get even.