Hacking is a dangerous activity. Due to the inevitable fact that the human brain has to be linked to the machine the flesh is in danger as well. Headaches that make one crawl up walls are a usual work risk; especially for the new kind.
Yet... The whole process is running on pure adrenaline. There is no time for thinking when doing a run. Not much at least. Movements are purely instinctive. Maybe that is also a big part of the show. Some cowboys are even dependant to experience the thrill at least once a day. Fortunately not all are on it like a drug. Those know how to judge odds instead of ruining themselves.
First step is to examine the system to intrude. For most places it is quite easy to get basic characteristics like their system states. As long as one targets a low security area that might actually be enough. However there are also high risk places; crowded by human and automatic defences. No defence is ever perfect however. If the timing is right one might be able to avoid some of the pests.
Of course it is best to actually avoid the security all together. For most nomal systems this should not pose a problem. Even normal ICE can be circumvented without too much trouble. At least most of the time. And if it hits you it is too late anyway.
Unfortunately there is also Black ICE and other hackers. If you meet one of them you better prepare for a cyberfight (see blue section for more details).