The first mistake was a howler. Lefty opened 2H, preemptive and partner, in fourth hand, bid 4S. It was passed around to righty who doubled. Back around to me. I was void in spades and 4-4 in the minors with a decent hand. I should have left it in, of course (4S goes down 1, perhaps) but I scrambled with disastrous results. Lesson learned -- a 7-0 fit is easier to play than a 4-3 one especially if the 4-3 contract is one level higher.
The second mistake, a closer call (I think), was on this hand. I was sitting South, and my 2H overcall shows hearts and a minor. The opponents end up in 3NT.
I reasoned that West probably had the hearts stopped, what with my hearts being so bad. And my diamonds were longer anyway. So, I led a diamond. Disaster ensued as declarer now had his nine tricks. (Our team-mates were in a club partial, making.) Do you have any way to deal with this? Does North have anyway of suggesting a heart lead?
These two hands cost so much -- 22 imps! -- that two of the teams we beat earlier pipped us, and we ended up fourth. Being a C-team, however, has its advantages -- we still qualified. It would have been better, of course, to have made it honestly instead of relying on the handicap.