What was going on here? I was sitting North-South with Paul Laliberte and east was dealing, with East-West vulnerable:

                                   NORTH (me)
                                  ♠️8 4
                                  ♥️ 6 4 3
                                  ♦️ 3
                                  ♣️ A 10 9 8 4 3 2

WEST                                                                 East
♠️ K 6 3 2                                                         ♠️ Q J 9 5
♥️  9 8                                                               ♥️ 10 5 2
♦️ A 7 4                                                            ♦️ K 10 9 2
♣️ K J 6 5                                                          ♣️ Q 7

                                   SOUTH (Paul)
                                  ♠️ A 10 7
                                  ♥️  A K Q J 7
                                  ♦️ Q J 8 6 5
                                  ♣️—

The bidding proceeded as follows:

East                  South          West           North
Pass                  1♥️             Pass          2♥️
Pass                  3♦️             Pass          4♥️
All Pass
Opening lead: ♣️5

What did Paul’s 3♦️mean? And how could I bid 4♥️  with only four high-card points?
The 3♦️ bid was a “help-suit game try.” Paul needed help in diamonds, and he wanted to know how many diamond losers I held.

My instructions: with zero or one diamond loser, even with six HCP, bid 4♥️ . With two diamond losers, evaluate your hand. Typically, if you have eight or nine HCP, bid game.  With three losers in diamonds, retreat to 3♥️  even with eight or nine HCP. So my task was simple with one diamond loser — even with four HCP —  bid 4♥️ .

West led a club to the ace, Paul discarding a spade. Declarer now led the ♦️3 to set up ruffs. West won with the ace and made a big mistake. Rather than lead a heart to limit ruffs, west led a spade to the ace.

All set up, Paul conducted a six-trick crossruff, ruffing three diamonds and three clubs, before crashing the ♥️A and ♥️K for 10 tricks. Game bid and made with 21 HCP.
Learn about help-suit game tries. They can only benefit you.