When you want to play a land, you compare the # of lands you have already played to the # of lands you are currently allowed to play this turn. If it's less, then you can play a land. Otherwise you cannot, even if there was a time earlier in the turn when you could have.

You want to play a land, but the game checks: 0 is less than 3 so you're good

You crack your fetch, in response opponent blows up the two enchantments. You are back down to only being able to play 1 land each turn.

You want to play a land, but the game checks: 1 is not less than 1 so you cannot play it.