With two known cards there are 50 x 49 / 2 = 1.225 combinations of starting hands, any other player can have. If we have AT, then 36 of these are going to be AJ-AK and 24 are going to be TT-AA. So the risk any random opponent has a better hand than AT is 60 / 1.225 = 4,9% or in round numbers 5%. Technically 22-99 are also "better hands", but here the equities run so close, it does not really matter. Those 60 combos are the ones, we dont want to see. And even though the math is not quite that simple, with 8 players left behind the risk someone else has AJ-AK or TT-AA, when we have AT, is close to 8 x 5 % = 40%.
I agree with the statements above - I don't necessarily worry about players waking up with a better hand behind me - I play proper ranges and if I face a 3bet I just play accordingly - I ditch the hands that have poor playability and marginal equity pre flop and call with the ones that will play best post. There are also plenty of charts and matrix forms that will tell you what to play vs a 3bet as well. You can make your adjustments from there.
Particularly when facing an UTG open, in theory, any 3bet that comes should be relatively strong because your opening range is the tightest at the table. This doesn't mean villans won't flat you with better hands tho - for instance PIO likes to flat a TON with AQ and AJs to an EP raise - simply because a 3bet may cause the EP player to do alot of 4betting - thus pushing us off of our equity, and even when they call us, our hand could still be dominated or behind their 3b calling range.
One more example - for the same reasons icmizer doesn't like jamming the smallest pairs on mid-short stacks (30bb or less) to an EP raise - if we shove 30bb with 33s from the SB to an UTG open - when we get called we are either crushed, or flipping at best - because UTG ranges generally aren't opening worse pairs from that seat.
On the preflop, each hand has approximately equal chances of success! It all depends on the position of each player in the tournament. If you can open or play connectors, this is one situation, if you survive, AT is a very good hand for the game and this is another situation. Do not overestimate any hand too much. It's nice to see A or pictures in hands, but more importantly, what shows you the flop, who you are in the game against and how you are able and can play. Sometimes you get KK, you see the flop and the size of the opponent's bet and you understand, that it is better to fold now and save your life... Therefore, pay attention to the little things in the game, they help to understand and see more than just 2 cards you have...