A Moderate Fit is Better than No Fit At All

A 9 5 4
3
K J 6 4 3
Q 8 3
10 2 Q 7 6
K 9 7 2 A J 6
A 8 7 10 9 2
A K 6 4 J 9 7 5
K J 8 3
Q 10 8 5 4
Q 5
10 2 Vul: Both

Bidding Box
SouthWestNorthEast
Pass
Pass 1 1 2 *
2 Dbl All pass *Inverted minors

South's incautious two heart bid (doubled) led to a score of less than 2%! While a second look at the hand shows that -- through a congeries of lucky breaks -- not only is 3 diamonds makable, but so is three spades.
So it wasn't South's entry into the bidding that was so disastrous, exactly, but that he offered only an inferior suit when he had another suit to offer. A double of two clubs here would have been a responsive double (by partnership agreement), showing hearts and spades. If you don't play responsive doubles, you could still run from a 2 heart double to 2 spades. I would never run from a double if my partner and I had time to find our best fit. But here the two heart bid doesn't qualify as indicating North-South's best fit, was not reached after a bit of exploration, and I would chance finding a better fit in spades vs. the possibility of pushing our bidding to the three level in hearts if that's our best suit after all. Which would make me very unhappy. However, South has only one more heart than spade, and I would hate to bank everything on a tenace-ridden 5-card heart suit, hiding a fairly good spade suit from partner. (Responsive doubles go hand-in-hand with takeout and negative doubles. When you see a hand where a convention would have been valuable, you can think of learning it.)
In any event, the point here is that South's hand becomes considerably more biddable if he can offer both suits in one whack. There is nothing like a fit to enhance the value of a hand -- here by three tricks. That should be as big a priority in your bidding as determining just how much high you might go.
The hand was really a good fit masquerading as a misfit. It was up to the partners to find the bidding methods that would smoke out the fit. Aside from responsive doubles, a run to 2 spades only risks one level in hearts if that's our best suit after all vs. the luxury of finding a (considerably) better fit. Indeed, all bidding is risk, including a pass.