To be responsible a person needs to understand how his acts would lead to consequences. He also better know how to make good decisions, so his acts would have expected results. I can say that to be responsible a person needs to make good plans, good decisions, and be able to simulate how events can unfold.
So an irresponsible person probably fails if he wants to plan or to simulate something. Inability to make successful plans would lead to inability achieve many goals which require several steps to follow. Inability to imagine results of different actions would lead to lack of understanding how to choose a better alternative and how to make a better decision.
Thus an irresponsible person would make his own life harder. But he can also fail plans of other people when these plans would be affected by his irresponsible behaviour. It means that irresponsibility is dangerous not only for a particular irresponsible person, but for the whole society this person lives in.
Fortunately planning and simulating can be taught. So if a person isn’t extremely carefree, if he or she wants to improve something in life, skills of planning, decision making and imagining outcomes would likely make the person more responsible. Of course each of these skills can be divided into a number of sub-skills, many of which should be studied and trained in real-life situations. But even if it takes time, making a person more responsive looks very doable.
At the same time people can’t always be fully responsible for everything they do, even if they want to be as responsible as they could. It happens because we can’t account for all possible scenarios and outcomes while planning something. As a result, even the best plans fail from time to time.
A realistic example of this is doctors. They want to make people better by improving their health, but people still die in the doctor’s hands. It happens because they could make unintentional errors which leads to worse decisions. Still doctors are very responsible persons because they know how important their decisions are.
So even if you can’t be one hundred percent responsible every moment of your life you still can improve yourself studying decision making, planning, and simulating outcomes.