Ax, Ax, Ax again, How much more money more until I learn?

I got 13th place yesterday in the Stars $100 rebuys, blinds were 1k-2k with 100 ante, I was the short stack with 18k and decided to go all in UTG with A7; we were playing 6 handed in my table, so I thought it wasn't that bad, but the button wake up with KK and I was gone. The problem with A7 or Ax for that matter is that when called you're a huge underdog almost always, there are still some donks who call all ins with KQ, KJ or 98s, but even there you're not that much of a favorite; and if not called what's the use of having A7, if not called you can have any hand; so in general I think it's better to go all in with JT,J9,T9,97 or the such than with Ax; besides I was UTG, with everybody still to act, it's better if you're in the button, since then look more like a steal and you have people in the blinds calling you with K high; and despite the fact I was the shortstack, I still have 9 BB and I'm a good short stack player. Ax has been my demise in so many tournaments and has cost me tons of dollars. I still remember my 2nd place in the big Sunday tournament in Party, 2nd place was 39k and first 72k; I went all in with the same A7 and my opponnent had AK and I lost 33k in the process. There was still one more time I lost with A7 in a big final table of a $200 tournament and went all in vs QQ and got 4th; and some other times I lost with A6,A8. Definitely of all the poker hands this is the single one I have misplayed the most. And my ignorance has cost me thousands of dollars. Ignorant people always suffer. Did I mention I still don't know how to play Ax?