how you can break a limit mentally?

Hey guys, My lifetime best in 100m backstroke is 1:00.09 (SCM), I swam this time with 21. Since I start swimming in masters competition, in my early 30s, my 100m backstroke times were around 1:03. I could droped my time this year to 1:01. (I am 37 now). And last weekend I swam my personal "masters" best time: 1:01,16. This race was not optimal, two turns were bad and my finish was bad too. I was in good shape and was try to swim around 60sek. Going sub 1minute in 100m backstroke was and is still a dream for me. And thats the point. How can you just stop dreaming and see things realistic and try to set goals that are reasonable? Is dropping one more second a realistic goal? I dont know. I am not trying hard, as I could to reach this (sub 1 minute), but I have a feeling, if I could do this, I will fail short once again... If I try somethings, that is near to my dreams, I fear that I get automaticly in my old wrong mindset, where I failed so many times in my young ages. Can you just reach a goal, without thinking of it? Maybe there is some mentally approch to this issue?