I struggled with this for several months after moving to ICU nursing. While I have encountered the rare individual who simply does not seem to learn from experience, most people do. At first, everything in the ICU is so overwhelming, task based nursing is pretty much the only way one can cope! But once the tasks themselves are easier to handle, you can start flying on autopilot and focusing more on the big picture. Furthermore, as you experience more and more situations, you will begin to develop a greater awareness of your patients.
Let me give you an example. Not too far into ICU nursing, I had a post surgical patient who was breathing pretty fast. He was hurting, so it didn't concern me initially. I asked if he felt short of breath or if he was just hurting. He assured me he was just hurting. The pain medicine ordered was not relieving his pain, so I finally called for new orders. I mentioned to the physician the patient's respirations had been around 30 for a while, but like me, he chalked it up to pain. After giving the new meds, the patient reported his pain was better. Now I was starting to get concerned because he was still breathing really fast. I asked again if he felt okay. He assured me he felt much better. His other vitals were great, heart rate and rhythm perfect--absolutely no signs/symptoms aside from tachypnea. My gut was telling me something was wrong, but my lack of experience was leaving me without answers. I decided to draw my AM labs just after midnight and this guy had a potassium around 7.0. I immediately called and got orders to fix him, but in the few seconds it took me to draw up insulin, this patient went into vfib and coded. Of course, then it hit me that the patient had been acidotic and he'd been breathing fast to compensate, but having never seen such a case without any accompanying symptoms, that hadn't even crossed my mind.
Another night later on, I walked into a fellow new ICU nurse's room to help her turn her patient. The patient had been fine, but I noticed she was breathing really fast. The nurse said she'd denied pain and everything else was fine. Given the experience above, bells and whistles were going off in my head. I knew this patient was acidotic and we were able to get a blood gas and determine the cause long before it became a serious problem.
An experienced ICU nurse might say "Well, duh!" But, for the noob, you have to have some bad situations before you learn to recognize when patients are heading in that direction.
You'll get there!