All in EV and Variance.. am I understanding it?

Just trying to wrap my head around all in ev. Here is how i think about it, basically its how good you run, ie having the best hand preflop to the river. My questions are:
1. Do I have the right idea here?
2. How much does it matter?
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As for my understanding of variance. Basically getting unlucky i.e having a made hand (that is a favorite to a draw) getting outdrawn, AA getting cracked by A6.