Hmmmm... good question. I think for me, it was this past summer - so DD was 20-22 months. We went through a string of EWs and such, but then we moved in mid July, and somehow, hit our stride. L's sleep habits became a little more "grown up", so to speak.. as in - if she EWed one morning, she'd ask for an earlier bedtime. Or if she had a late morning, she'd shorten her nap on her own. Things that naturally just made sense, but that I didn't necessarily have to dictate. So I'm a lot less concerned now about her day sleep and night sleep... sometimes she has short nights, sometimes she doesn't... but it all seems to even out in the end. Because of the holidays and travelling and such, we've had several "odd" days/nights - a 15 min nap, 2-3 hr NW because of a redeye we took, etc, etc... and it didn't result in much more than an earlier bedtime or nap.
So for me - it was really a result of *her*, if that makes any sense. If I had a toddler who was still really having a hard time with regulating sleep - EWs or NWs or whatever - and it was affecting his/her sleep, then I probably would still be stressing quite a bit...