Many people have some level of preparation for a short-term crisis - say, a temporary power outage. Others who live in areas with known risks like tornados, hurricanes, or earthquakes may have a higher level of preparation, but probably nothing that would sustain them for more than two weeks.
It is important to consider, then, the possibility of a Long Emergency: a critical event causing crisis conditions for periods of months to years. Here is one plausible scenario that should get your attention: a coronal mass ejection (CME) from the sun, striking the earth so quickly that there would be little to no warning. It would fry the electrical grid, plunging the world into a pre-electricity era. Estimates for a full recovery in the United States range from 4 to 10 years.
It's important not to be overwhelmed by these possibilities. While such an event would no doubt impose severe hardship on everyone, there are ways to increase your chances of survival. Everyone should think in terms of the essentials: shelter, food, water. You can purchase water filters and pumps so that, if the tap water becomes unsanitary, you can make it suitable for drinking. You can store food and learn how to grow your own food. You can purchase solar panels (for less than you might imagine) in order to give your home a limited amount of electricity -- enough to sustain refrigeration, for example, by powering your refrigerators for a few hours a day.
I think it's important to approach crisis preparedness with a problem-solving mindset, and to not be overwhelmed by all of the possibilities or by the difficulty of preparing for a life off the grid. Simply cultivating an awareness of all the ways in which we are dependent upon electricity and other vital services, and then coming up with an alternate plan for replacement of those services, will go a long way.