100%
Even the best players miss lethal in complex situations. Particularly calculating buffs, favor gain, sanctum interactions, etc. It can get complicated, but it's a good idea to start every turn checking for lethal. Even if it's just a mental note at 30/30 of "nope". It builds good habits.
Very true, the more you do it the better you become at it. And the faster you can do it. Eventually, it becomes second nature to you. And that is the goal. =)
I remember when I used to play Go. And I was starting to count territories. And How the world opened up to me when a friend told me to count them 2 and 2 instead of one and one. Basically cut my counting time in half. Small tricks like that. =)