Spurs 14-26 from 3 1st half for 53%
Then 3-17 from 3 2nd half
Very Celtics like 
So 17 for 43 for the game, 39.5% overall. Seems like they shot the 3 pretty well overall. This is how the element of chance works. 17 3s in a half is not that many these days. The discrepancy in make % is striking, but I don't see the issue being they took too many 3s in the 2nd half. Another way to look at it, they missed 12 3s in the first half and 14 in the second. If they had gone 12-26 in the first and 5-17 in the second, does that change anything?
I think what this continues to show is that the swing or variation in 3P% in the playoffs can be much wider than what is typical in the regular season. It makes some intuitive sense although I have not done a dive into the stats, just observing this anecdotally. So does this mean a team should take fewer 3s in the playoffs if that is what got them there? Take fewer in the second half than the first, expecting that you will miss more due to pressure? Everyone keeps bashing coaches for this but I am not sure what you really want them to do.